A city in bloom: much more than a seasonal flowering

''Miracle'' might be a touch too strong too describe what many people here consider the ''New Philadelphia.''

But as ''Rocky III'' -- the latest in the series of movies about the good-hearted Philadelphia prizefighter starring Mr. Stallone -- gets ready for its debut at theaters across the country, you might say that Philadelphia is beginning to bloom on every conceivable front.

Oh, yes, it's soon the time when hundreds of varieties of azaleas bloom behind the art museum and regattas of sculls take place on the Schuylkill River, summoning sightseers from the world over. But the new roots of Philadelphia's prominence run deeper than mere seasonable flowering.

They are traceable to the nation's Bicentennial six years ago, when this somewhat insular, self-effacing, and at the same time immensely proud and vibrant city started to come out of its shell -- and has not gone back into it since.

City officials, aided by a zestful private sector, worked around the clock so Philadelphia could put its best foot forward for the Bicentennial: Streets were repaved; the 548-foot-high City Hall spruced up; restaurants opened by the score; and Frank Rizzo, then the mayor, who could be as acerbic as any public official in America, greeted the millions of tourists with warmth and enthusiasm. Philadelphia glimmered briefly in the spotlight of the national news media and in the heart of the nation born here.

But behind this facade and fanfare, many native Philadelphians knew another, much sadder Philadelphia in turmoil -- an older industrialized city of the Northeast with a dwindling manufacturing job base; a city torn apart by racial violence, with some officials predicting it was swiftly heading toward a ''police state''; a city of old, run-down neighborhoods, left to decay in the wake of white flight to the suburbs; a city of substandard housing for many minority residents; a city with a downtown area shunned in favor of suburban shopping malls. The city's budget was ballooning out of control and was, a few years later, to bring on the threat of brankruptcy.

Thus, the turning point for Philadelphia seemed to be a sort of convergence of the best and the worst during the same year. The Bicentennial highlighted Philadelphia's strong points -- its unequaled historical significance and the small-town flavor it retains despite being the nation's fourth-largest city.

On the negative side, more than 200,000 Philadelphians signed recall petitions against Mayor Rizzo. While only 145,448 signatures were neccesary to recall him under the city charter, the petition drive lost because, impartial close observers say, Rizzo-controlled city commissioners found fewer than than this required number were valid.

Mr. Rizzo remained in office until January 1980, when the clean-cut William J. Green Jr., who has come to symbolize much of the ''New Philadelphia,'' was inaugurated as mayor.

But the forces of change had begun to take shape before then. The city began recognizing the need to make its many assets known, and for the first time the government is starting to help the private sector pay for advertising.

Restaurants and hotels blossomed, and new offices, aided by a favorable tax climate, climbed skyward.

The Philadelphia Industrial Development Corporation (PIDC), the city's main business development arm, stepped up its campaign of helping many of the city's industrial and commercial companies not only remain here and not flee to the suburbs or the South or Southwest but expand as well.

PIDC figures show it facilitated 250 plant expansions and relocations in 1981 alone, says Charles Pizzi, the corporation's marketing manager. ''Unfortunately, however, the only thing that makes news locally is the plant closings.''

Indeed, there have been dozens of plant closings in the past five years. Thousands of manufacturing jobs have disappeared. In the past year, unemployment here, as elsewhere in the country, has soared.

Serious minority unemployment problems are only hinted at in the official figures, declares Robert Sorrell, president of the Philadelphia Urban League. Unemployment among young working-age blacks is probably over 40 percent. Now faced with cutbacks from Washington, city fathers say teen-age black unemployment will be substantially higher this summer than it was in previous years.

But Richard A. Doran, the city's commmerce director, remains optimistic. It's his firm belief that the 1970s were a kind of ''shaking-out period,'' which saw the last major chunk of manufacturing jobs lost though plant closings and migration to the Sunbelt, and that many companies that have continued to weather the economic storms -- from national recessions to uniquely local problems -- will stay put and possibly expand sometime in the future.

Moreover, he is proud that a growing number of companies in the suburbs have ''decided to expand and relocate in Philadelphia,'' although he adds that he cannot be sure this will be a lasting trend. Yet since the beginning of December , five suburban firms -- all helped by the PIDC -- have moved into town with ''nearly 400 jobs involved in the transactions.'' He adds, ''Nearly 200 of those are newly created.'' Perhaps even more important, ''The vast majority of these jobs are targeted for Philadelphia residents of low and moderate incomes.''

As for companies already in Philadelphia, Mr. Doran and other city officials want small and medium-size businesses to receive the lion's share of city financial help first. That coincides with the basic character of business in Philadelphia: It is a city of mainly small and medium-size businesses, many of them family-owned.

And even some of Philadelphia's industrial giants, such as the Sun Company Inc., one of the nation's major oil companies, have retained some of their family ties. There was a time when more than 30 Pew family members were involved with Sun, which up until 1976 was called the Sun Oil Company. Today that number has dwindled to half a dozen or so.

Meanwhile, the service industry continues to make strides here - though still not marked enough for some highly respected local economists here, such as Gerard Adams of the University of Pennsylvania here.

Dr. Adams told the Monitor that Mayor Green's administration has ''not yet moved to get this economy moving again'' and that increases in the service side of the economy have fallen far short of ''taking the place of the old industries'' which have closed or moved.

But Dr. Lawrence R. Klein, also a professor at the University of Pennsylvania and a Nobel Prize-winner in economics, says that there are a number of signs pointing to a brighter economic future here. Among them, he said, was the recent surge in the number of high-technology enterprises.

Another reason he expects Philadelphia to ''probably do better than the average city in the Northeast'' is that the ''City Center area is hospitable. . . . Everything is easier to do here. . . . There are no long lines . . . . It's more friendly.''

Dr. Klein's comments were repeated continually by people I met here, including transplanted New Yorkers, grateful to have left jangling Gotham, and even some Californians.

Other signs pointing to a brighter economic future:

* Tourism officials are hopeful that 1982 will be the year Philadelphia breaks its Bicentennial record of 4.2 million visitors.

The ''Century IV'' celebrations will be an obvious drawing card this year, but officials expect the city's restaurants, hotels, and theaters to help lure out-of-towners, too.

* The University of Pennsylvania. The university, the largest private employer within the city, continues to make new contributions to the city's economy and position as a major learning center. Much of the growth in high-technology concerns here is related to the university's own movement in this direction. It has also served as an anchor for housing renovation efforts that are cutting into some surrounding slums.

* Neighborhood development. Philadelphia, often called a ''city of neighborhoods,'' is making steady strides in ''building on areas of strength,'' as one city development official put it. Germantown, with its plethora of distinctive mansions abutting some of the city's most ramshackle housing, is once again becoming home to the kind of middle-class professional people who fled it amid the racial tensions of the Rizzo years. Even North Philadelphia, which ranks as one of the Northeast's biggest black ghettos, is seeing some improvement, as some rubble-strewn vacant lots become pocket parks and urban homesteaders move in.

* Philadelphia's restaurant renaissance in full bloom. More than 375 new eating emporiums opened since the Bicentennial. The key ingredient in Philadelphia cuisine is variety -- not only from one restaurant to another, but on the same menu. And it's not just haute cuisine, it's big bucks: The restaurant industry now employs more people than any other sector of the city's economy.

* Many sportswriters rank Philadelphia first in the nation. Just try and get a World Series ticket to a Phillies game. Fans of the Stanley Cup-winning Philadelphia Flyers are just as avid, as are 76er basketball enthusiasts.The movie ''Rocky'' captured not only some of the city's sports enthusiasm but, in a way, some of the spunk and spirit of this entire historic city -- a city that is now definitely past the crossroads of change and is slowly coming into its own undisputed national prominence.