Bang-up centennial at the Pops 100th birthday at the Pops The Pops starts a new century Pops celebrates 100 years. A gala opening tonight and a 15-city tour kick off a new century for a thriving Boston bastion

For this city, it is part of the natural rhythm of Spring. Swanboats appear in the Public Garden, magnolias blossom along Commonwealth Avenue, and one of the world's best orchestras -- the Boston Symphony -- metamorphoses into ``the Pops.''

Ninety-five first-rank classical musicians doff black tie and tails for sport jackets in restaurant-waiter blue. For two months, they shelve Beethoven, Bach, and Brahms and dust off John Philip Sousa, light Viennese classics, pop/rock/jazz, and film and Broadway tunes. In highly stylized symphonic orchestration, they celebrate Gershwin to Porter, Rodgers to Sondheim, with a festive flair that allows both audience and musicians to ``let the hair down and roll the shirt sleeves up.''

Tonight, when local glitterati throng into the classical Symphony Hall -- whose normally staid interior is festooned with baubles, balloons, and mirrors that shimmer across tables of Havarti cheese and supersweet punch -- more than just a city will join in the hoopla. People in far corners of the globe will tip their hats to the world's most recorded and widely heard ensemble as it reaches a milestone centennial year.

A peek at the telegrams that poured in in 1979, when late maestro Arthur Fiedler celebrated 50 years of conducting the Pops, hints why the Pops has become so venerated.

``I continually thank God for Arthur Fiedler, at whose hands I first heard live orchestral music,'' wrote composer/conductor Leonard Bernstein. ``You have done more to popularize classical music than anyone I know,'' wrote jazz great George Shearing. ``It is impossible to evaluate the happiness and pleasure you have given to so many through more than half a century,'' wrote conductor/arranger Andr'e Kostelanetz.

Today Fiedler's work is still appreciated. ``The influence of the Boston Pops is quite astonishing when you consider that practically every orchestra in America now does pops concerts in the formula developed by Arthur Fiedler through the 1930s and '40s,'' says David Tomatz, director of the School of Music at the University of Houston.

The Pops's popularity continues unabated five years after Fiedler's passing. Through countrywide performances, a regular PBS television series, films, and more than 50 million records sold, the Boston Pops remains the country's first, oldest, and still leading ``pops'' orchestra. That means, in the words of BSO founder Henry Higginson, making ``concerts of a lighter kind of music'' accessible to the broadest possible public.

The now famous tripartite formula includes: a group of shorter, light classical works, overtures, marches, waltzes; an appearance of a soloist, often in a complete concerto; and finally a group of pieces selected from the wide repertory of current popular songs.

In 1980, the Fiedler baton was handed to John Williams. A four-time Oscar winner, veteran of 60 film scores, including the five top money-grossers of all time, Williams has helped the Pops expand its legacy to include more film, Broadway, and show-tune music -- and original compositions by himself and other top name composers, such as Peter Schickele and Peter Maxwell Davies.

``By performing popular music so wonderfully, by setting such a high standard, they've set a standard for the entire industry,'' says Mr. Tomatz.

Beyond the special festivities of opening night -- James Galway, Cleo Laine, and the premier of P.D.Q. Bach's ``The 1712 [sic] Overture,'' discovered by Professor Schickele -- a full season of celebrations will take the orchestra well beyond its hometown. A 15-city, transcontinental tour will include two free concerts: one in New York's Central Park July 8, and the other at the Lincoln Memorial July 14.

Two recent digital record albums by John Williams and the Pops for Philips are also doing extremely well on the charts. ``With a Song in My Heart'' features soprano Jessye Norman in favorites by Cole Porter, Jerome Kern, and George Gershwin. One cut features John Williams on piano. A second album features Prokofiev's ``Peter and the Wolf,'' with narrator Dudley Moore.

In the 100th-anniversary year of such a successful enterprise, it is interesting to note that the Pops arose partly as an extension of the regular symphony season to keep musicians on the payroll between summer and winter seasons. As such, the BSO was 70 years ahead of its time, avoiding the crises that hit practically every US orchestra in the 1960s, when musicians clamored for year- round employment. Because of sold-out houses during the tourist season, plus recording revenue, the Pops, unlike the BSO, brings in more than its own operating costs. Both rely heavily on gifts and endowments.

Though some musicians don't admit it, the 10-week Pops season is a welcome respite between the winter and summer schedules. Seventy-five concerts of more serious fare are performed in the 22-week winter subscription series. And then, after playing six nights a week as the Pops through May, June, and early July, the BSO begins the summer outdoor season at Tanglewood, in the Berkshire Hills of western Massachusetts. (Since the local popularity of the Esplanade concerts along Boston's Charles River has grown, a second orchestra, made up of top Boston free-lance musicians, plays some of the Pops's free outdoor concerts.)

Discriminating listeners wonder how much of a toll this year-round schedule, along with cabaret conditions and shortened rehearsal time, takes on Pops players.

``You have these fine musicians that are trained to play precisely with beauty and finesse told that fine nuance makes all the difference, and held very severely to that standard,'' says Michael Steinberg, former Boston Globe critic, now artistic director of the San Francisco Symphony. ``Then suddenly for seven or eight weeks you plunge them into the bucket where nothing much makes a difference because the audience isn't listening as closely. That has to make a difference to the players.''

``There will always be a place for the Pops,'' retorts Harry Ellis Dickson, a 48-year veteran and associate conductor of the orchestra. ``Of course there are people sitting at tables eating and drinking and waitresses clanking punch bottles. But it's part of the charm of the Pops that no one is as stiff as [in] the regular season.''

With all the success of the Pops, observers are asked why the formula doesn't seem to translate to other cities, other orchestras. The answers come under two broad categories, tradition and commitment.

``You have a funny collection of elements in the Boston Pops, which, from the outside, don't appear to go together,'' says general manager Tom Morris. ``You have a world-class orchestra, with a separate conductor fully committed to make a separate repertoire work. You have one of the world's great concert halls and a cabaret setting. Somehow you put all those elements with a very broad musical repertoire and very relaxed atmosphere, and it works.''