Those colorful Puritans? Yes, say scholars, and here's an exhibition to prove it.

A New England Puritan of the 1600s was someone H.L. Mencken equated with ''the haunting fear that somewhere someone might be happy.''

The Museum of Fine Arts in Boston is prepared to announce that the much-maligned Puritans have had a poor press.

For five years Jonathan L. Fairbanks, curator of the museum's Department of American Decorative Arts and Sculpture, has had 17th-century New England under the microscope of a team of experts - art and cultural historians, folklorists, demographers, archaeologists.

He is now poised to lift the curtain on an entirely different, radically brighter view of these people who were among America's earliest colonists. The show, a 500-object exhibition, will run here from May 5 to Aug. 22. It's called ''New England Begins: The Seventeenth Century, 1620-1700.''

Mr. Fairbanks believes the exhibit's scholarly catalog, written by specialists in many disciplines, will hereafter be the basic text for 17 th-century art and culture. ''Anybody who is going to write about the first period in American art is going to have to turn to this catalog.''

He promises the exhibition will be full of surprises, and will ''very considerably change our perceptions of that century.'' Based on broad research and new discoveries, it will, he avers, explode the myth of the Puritan Englishmen who settled this intellectually and politically yeasty corner of the country as straitlaced, dour-faced, drably donned, and uncomfortably housed.

That popular perception is based, he says, on Victorian novels such as Hawthorne's ''The Scarlet Letter'' - stereotypes that Fairbanks insists ''are simply not true.''

''That this was a dull, drab society wearing all black and white is ridiculous! These people were full of color, slashed sleeves, lace, brilliant reds and greens. They loved color and decoration in the 17th century. They were not plain people. They were elaborate people.''

Oh, it's true, he concedes, that there was a very special ''vogue of melancholy'' in the 1600s, and some melancholic types did wear black exclusively. ''But that certainly wasn't a style that was rampant throughout New England. The style that was rampant was as much color and rich ornament as a person could manage.''

One has only to think of the late Elizabethan period and of Queen Elizabeth in her bejeweled and brilliant costumes, he says, to see how that style had trickled down to the middle class by the time the Puritans dropped anchor in Boston Harbor.

But what about those ''sumptuary laws'' passed to restrict people from wearing garments beyond their rank in life? ''They tried to enforce them, but it just didn't work in a free society,'' he chuckles with thinly veiled glee. ''Those laws couldn't really control human beings. Being human, they wanted to show off, so they wore things beyond their proper station.''

As an 11th-generation descendant of the Fairbanks family (its 1637 home in Dedham, Mass., is the oldest standing wood-frame house in North America), this namesake of the original Jonathan Fayerbanke reports with some pride that one of his own ancestors was fined a few shillings for wearing great boots before he was supposed to be able to afford them.

New Englanders of the 1600s ranged from people of high station and considerable wealth to those of lowly circumstances. None of them were of courtly level and probably few were of peasant stock. ''They were of the middling sort,'' Fairbanks explains. They were also highly literate - 80 to 90 percent could read and write. Bible reading in their homes was a must, he says, and he links their education to that practice.

The central message of the museum's broad-ranging study of the period is that as soon as they arrived, the Puritans quickly imposed a complete culture on the New World.

The vast new continent had little effect on their tastes and mode of behavior. Far from being a deprived frontier lot satisfied with rough standards , they were determined not to get lost in this wilderness. They carried as much cultural baggage as they could manage in order to continue their manner of life.

By 1675, there were only 1,500 families in Boston - about 8,000 residents. ''But the vitality, the number of ideas that were being generated, and the amount of human activity here were really very remarkable for the number of its people,'' Fairbanks says. ''Take any suburban town today that is much more populous and compare what's coming out of it intellectually.''

In 1636, only six years after Boston began, Harvard College had been founded across the Charles River in New Towne (later Cambridge).

Four years after that, a press had arrived and had begun churning out books. As the museum exhibition will show, the Puritans' material possessions - clothing, paintings, ceramics, furniture, architecture - reflect their familiarity with the mainstream traditions of Europe.When they set sail for the land of the Pilgrims (who settled Plymouth in 1620), the Puritans also packed their skills, systems of design, and their notions of shape, form, and ornament.This style, called ''Mannerism,'' began around 1520 as a late episode in the Italian Renaissance. From there the style migrated to Holland, then to England, and from there to America. ''We have been able to demonstrate this over and over again in paintings and furniture and architecture,'' he says.A tall silver cup made in England in 1610 and handed down through the family of Massachusetts Gov. John Winthrop is a prime example. Brought here by him, it is richly worked in Mannerist details. A remarkable specimen of style transfer, the cup was the latest fad in England when the Puritans departed for the New World. Similar cups were being carried by English ambassadors as diplomatic gifts to Russia.Mr. Fairbanks, an authority on American furniture, wrote an essay for the show's catalog analyzing how 17th-century American artists painted. His original research has broken new ground.One of the oddities of the 1600s is that painters in Boston - and this is where all New England painting was being done - dated their works but rarely bothered to sign their names. What was the point of signing them? Everybody knew everybody else.In attempting to identify groups of paintings as the work of different artists, Fairbanks became intrigued with the proportional system those portraitists used. Robert Trent, a doctoral candidate in American studies at Yale University who has written essays for the catalog on the concept of Mannerism and 17th-century furniture, was convinced that paintings, like all other works of art of this period, were based on proportional systems that were part of the Mannerist tradition. He proved to be a good Sherlock Holmes. For example, if you are an adult of average proportions, your height is about equal to 71/2 times the length of your face. And your face, from chin to hairline, is the same length as your hand from heel to finger tips. In the 1500s a curator for the Medicis declared that the ideal body length is 10 face-lengths long. This he based on an ancient Roman standard. This system of proportion was a Mannerist convention.''I began to make measurements on portraits in the exhibition of adults and children,'' Fairbanks says. ''And, lo and behold, I found that figures in both are indeed extremely tall!'' Many adult portraits are 10 face-lengths in height. Children are 71/2 face-lengths long rather than today's average of 41/2 to 5. ''That explains why these children look to us like miniature adults,'' Fairbanks says. ''They have a normal adult-length body in relation to their face.'' The proportions of a child's face differ from an adult's. Children's eyes, for example, are in the center of their cranium. Painters of the 17th century understood this and put children's features on children's faces. The disparity Fairbanks detected was their treatment of the body vs. their treatment of the face. ''I don't think they considered it a distortion but an idealization,'' the curator says. Flying further into his ferreting act, Fairbanks also discovered why portraits of the 1600s look less natural than portraits today. New England painters were using systems of perspective that date back to late Elizabethan times. No matter how the sitter was facing, they made both eyes exactly the same size, and placed eyes, nose, and mouth precisely parallel to one another. Today this isometric perspective is associated with caricature in cartoons. A much more realistic system called convergent perspective had been invented in Italy in the 1400s during the Renaissance by Leon Battista Alberti. ''It was the beginnings of our understanding of how to manipulate the illusion of space,'' the curator explains.Under this system, eyes and other features are placed along lines that travel into space and converge at a point on the horizon. But in the English-speaking world, this system was not published until 1670. Some of the paintings in this exhibition were done on or before that date.The earlier system makes the paintings look very flat. But, says Fairbanks, ''they're only flat-looking to our eye that has been educated under the convergent system. But it didn't look flat to the 17th-century yeomen because they didn't know that system.''These discoveries are revolutionary in terms of American art history, ''because nobody has explained them before,'' Fairbanks says. ''Few persons have taken the trouble to look carefully at paintings made in America at this period. Most critics have just said that American painting begins with John Smibert (a trained English painter) coming to this country in 1729. We now know that three or four generations of painters were working in America before Smibert arrived!'' Meanwhile Mr. Trent has detected unexpected patterns in the construction and carving systems of furniture. All the crafts, he says, were laid out with ruler and compass, including their ornamentation. Almost all the ornament during this period is very geometric, he says.

These designs, seen in chests and other types of furniture in the exhibit, are suggestive of the counties of England from which each of these craftsmen emigrated. Just as there were dialects of speech, there were dialects of ornament. ''The difference between craftsmen working here and those in Europe,'' Trent says, ''is that the medieval man was using Gothic proportions, while the proportional systems used here were all based on classical architectural canons that again had been transmitted to New England from Italy via the Netherlands and England.''Wood was the plastic and steel of the 1600s, the Puritans' principal medium of expression. It was essential to the shaping of the colonists'world. And there was plenty of wood around.Typical of the huge land grants of the period were the 2,200 square miles given by the state legislature to Dedham, which lies 10 miles southwest of Boston. Officially, this big little town extended all the way to the Rhode Island border. But 40 years later, Dedhamites had settled only about one square mile.How did the Puritans feel about living on the edge of a seemingly endless wilderness? ''If you can imagine yourself on the moon, that might have been about the way they felt about 2,200 square miles,'' says Robert Blair St. George. He helps teach a course on the history of the American environment at the University of Pennsylvania and is working toward his doctoral degree in American folklore.In land-starved England the Puritans had had to rent land. Throughout the 1600s, farmland was free for the asking here. The colonists braved the Atlantic for various reasons: religious freedom, land, economic opportunity. Living on the fringes of what looked to them like infinity, the colonists firmly believed that America would never run out of land. But the word ''nature'' wasn't even in the daily lexicon of the Puritans, who dominated the early New England colonists.Their sense of land was highly restrictive, Mr. St. George says. The only part of the land they cared and worried about was the part that had been broken by their plows and fenced in. This had a function they could understand. The rest was to them ''a vast and empty chaos,'' as one author put it. Their tax rolls had two categories of land: ''cultivated'' and ''waste.''But the general belief that there was nothing but trees, trees, trees, is another myth, St. George says. ''The Indians had lived here and they practiced a slash-and-burn technique to make fields for planting corn. There were also open meadows. I think most scholars would agree that one reason settlement proceeded so quickly is that the landscape here was very much the same as that from which these English yeomen came.''Their houses, far from looking primitive, he said, represented the imposition of man's reason or artifice on a landscape that they read as unordered. ''What they did not want,'' he says, ''was a house that let them enjoy nature. They wanted one that did not remind them of working in the out of doors.''The English who settled Plymouth separated themselves from the Anglican Church and called themselves Separatists. The Puritans who settled the Boston area thought that they constituted the Anglican Church and were the only good part of it left. But the concepts of the early colonists on many subjects were changing so rapidly that looking back on their first 100 years, the historian finds paradoxes.For example, though the Puritans were reformed Protestants, they firmly believed in astrology. It wasn't until the early 18th century, St. George says, that ''the control of man's body was no longer perceived as being from the planets or the houses of the zodiac but instead the body was viewed as a self-contained machine.''The Museum of Fine Arts' exhibition on this rich and formative period of American life and culture is a joint effort. It is funded by grants from the National Endowment for the Humanities and FMR Corporation - manager to the Fidelity Group of Funds. Additional support has been provided by the Massachusetts Council on the Arts and Humanities.More than 130 museums, historical societies, and private collections have been drawn upon for loans to interpret the lives of yeomen, merchants, and Indians. In addition, many objects are recent archaeological discoveries in New England never seen by the public.Fairbanks, Wendy Cooper, the assistant curator of decorative arts, and their staff at the museum have collaborated with scholars from Boston University , the Society for the Preservation of New England Antiquities, and Plimoth Plantation. Scholars and students have scoured this region as never before to compile the most comprehensive survey yet of 17th-century material. The big surprise to everyone is the enormous amount of material that is available. Throughout the show, which will be presented in the museum's new West Wing, craftsmen from Plimoth Plantation will put on live demonstrations. But the main live event will be the raising in the museum's outdoor sculpture courtyard of an exact reproduction of the Fairbanks House. This is the same replica that was erected on Boston Common two summers ago to celebrate the city's 350th anniversary. Plimoth workers will wear their period costumes and speak the dialects of the various counties in England from which the newcomers emigrated.Several sister institutions in the Boston area have agreed to set up exhibits that will run concurrently with the museum's show.