Andre' Previn is the ultimate professional. And when he became music director of the Royal Philharmonic Orchestra 2 1/2 years ago, what he found was that a musician's lot is not always a happy one.

"It's a terrible life and it's unlike anywhere else in the civilized world," says Previn. "It's been this way in English orchestras for a hundred years. Bernard Shaw wrote an article about it at the turn of the century. Nothing has changed. Nothing! . . .

"I've been a player all my life. I cannot only sympathize or empathize with the plight of English players, I really identify with them. I just don't stand on a box and wave my stick. And I just thought, 'Can't we at least go down swinging.' "

Instead, Previn and the Royal Philharmonic, who perform at the Kennedy Center Wednesday night, have come up fighting. With a major music festival, their own record label and the first contract for orchestra players in English history, the RPO is forging a path out of the morass that London orchestras have fallen into. Its current American tour is the first under Previn.

"When, I first went to England in the mid-'60s," says Previn, "there's no denying that it was in most people's view the most interesting and thrilling music city in the world. If you didn't play in London, you had something wrong with your career. And although musicians worked just as hard, they were much more on top. It was a very, very exciting time."

Now, while London is still believed to have the best pool of talented free-lance musicians in the world, none of the orchestras -- the Royal Philharmonic, the London Symphony, the London Philharmonic and the Philharmonia -- has consistently maintained the international prestige they all once enjoyed. The players have been overworked, underpaid and dragooned into trivial musical pursuits.

Previn, 58, has conducted virtually every major orchestra in the world and has previously been music director of the Houston and Pittsburgh symphonies. He first gained recognition as a jazz pianist and composer of Academy Award-winning film scores, and has done numerous series for PBS and the BBC. He learned about the life of London orchestral musicians during his 11-year principal conductorship with the London Symphony, which ended in 1979.

But when he returned in 1985, he recalls, "I had forgotten how mindless some of the work is that they're expected to do. For instance, to go to three different places in one day and play at three different rehearsals, one of them as the accompaniment to a pops record, one of them for a children's show and then in the evening for Mahler Nine. I thought, 'This is absolutely crazy. This cannot go on.' "

On average, London orchestras will perform as many as 700 sessions a year, while their American counterparts will do about half that. "You can imagine what it does to the energy level of people to play two sessions a day, seven days a week, 365 days a year," Previn notes.

The longstanding financial insecurity of orchestra players is the root of the problem. Playing without contracts, London musicians are paid by the individual performance or recording. Without guaranteed income, they will book anything -- a repertoire they didn't want with a conductor they might not want, records they didn't need. The result, a musician's nightmare.

In comparing it with conditions in America, though, Previn does not say outright that everything is worse in England.

"Obviously the American side is infinitely better adjusted to the players' well-being and their musical interests," Previn says. "On the other hand, in England, the orchestras are all self-governing. They are in charge of their management, and here it's the other way around. So in England you don't have any of the occasional problems that beset American orchestras, which manifest themselves in the kind of thinking of 'It's us and them.' "

Like the other London orchestras, the Royal Philharmonic had been through a period of crisis.

After running large deficits and suffering from a lack of direction, Ian Maclay in 1982 became managing director and set the orchestra on firm financial ground. The level of play improved and it began attracting excellent conductors.

The Royal Philharmonic that Previn found had been tempered into one of the most self-confident yet friendly orchestras he had ever worked with. "They get along so well, they respect each other and they don't mind all the hardships," says Previn.

"They know what it is like to struggle through life, so they appreciate anything positive that happens to them," adds Russian pianist and conductor Vladimir Ashkenazy, who joined Previn at the Royal Philharmonic last January.

Putting London players under contract has been talked about off and on for 30 years. But Previn went beyond the talk. "When the Arts Council of the government is absolutely no help, we just have to use our own devices. I think it's the only way out for the future of English orchestras," he says.

Previn advocated a contract for the orchestra, and Maclay and the orchestra's governing board then developed a formula acceptable to the players. One problem, however, was that a contract required steady engagements. And when Previn took over the Los Angeles Philharmonic in October 1985, this became increasingly difficult.

Realizing this, Previn felt that a partnership at the top was critical. Previn suggested that Ashkenazy, a longtime friend who had already worked extensively with the Philharmonic, would be the one person with whom he could share artistic direction. After extensive discussions, all three parties agreed that Ashkenazy would become the music director and Previn would go "back to the time-honored nomenclature of being principal conductor, which didn't lessen my workload at all, but at least I didn't feel like I was a music director on paper but not one in actuality."

Ashkenazy's joining the Philharmonic proved the final ingredient. Early last November, the orchestra voted overwhelmingly in favor of the contract, the first such in the classical music history of Britain.

The transition from Previn to Ashkenazy as music director in late November was not a quiet one. Previn, a master communicator, seized the opportunity: In a long statement, he attacked "the squirrel cage" of orchestral conditions endemic in London, "with its absence of contract players, the lack of security and the lowest salaries paid to musicians in the civilized world. Because of this the orchestra's most pressing aim has always been to keep working."

Ashkenazy was entirely sympathetic. "It's just the feeling that we must try something," he says, "that we must make the player's life more comfortable, less histrionic, more palatable. I think the situation will be better under contract because they will have more free time: They can think more, relax more, breathe more."

The contract, however, is a financial gamble. "If we've guaranteed the musicians a level of salary they currently receive," explained Maclay, "and they're no longer working every hour that God sends, it means the orchestra is not earning income and we have to make up that income from other sources. And there are, of course, no guarantees that that money will be forthcoming."

These sources, according to Maclay, are the Arts Council of Britain, which the orchestra believes should provide more money because of these developments; increasing corporate sponsorship; and a separate Philharmonic Pops Orchestra, led by Henry Mancini.

"Should the year turn out to be very unsuccessful," adds Previn, "{the orchestra members} will have taken a tremendous financial loss. But I don't think it will and neither do the players."

With an established annual wage, the orchestra hopes it will now be able to accept or reject concert and recording dates on esthetic as well as financial grounds. Previn promises to try "more adventurous programming . . . things that are not played all the time." The need for more rehearsal time for such music "means they have to do less nonsensical work," he says. "You see, it all interlocks."

If things go well, he adds, "you can certainly bet that the other London orchestras who are watching our programs with a very careful eye will follow suit."

Results of the new contract are still a matter for speculation, but the Andre' Previn Music Festival has already established a strong record. In June, traditionally a slow month, it takes over the otherwise empty music halls on the south bank of the Thames: Festival Hall, Queen Elizabeth Hall and the Purcell Room. In the 30 concerts of the first festival, the orchestra played to more than 80 percent of capacity. By last June, in only its third year, the festival -- now called "The Previn Selection" and featuring jazz and other music in addition to classics -- had become the biggest attraction in the 30-year history of Festival Hall.

"They've been terrifically successful," Previn says. "And we do some pretty adventurous things there." Among these forays were entire evenings devoted to the music of Olivier Messiaen and the London premie`re of Peter Maxwell Davies' Violin Concerto commissioned by the Philharmonic in honor of its 40th-anniversary season.

In May 1986, the Royal Philharmonic launched another major venture under Previn when it debuted its own record label, RPO Records. Representing the best of what the orchestra can do, it doesn't preclude recording with other companies. But it does increase the orchestra's self-determination.

The RPO label has artistic advantages as well. With its own label the orchestra is free to record the music of its choice, especially neglected music such as Tippett's "A Child of Our Time" and Walton's "Belshazzar's Feast," the two records that Previn has so far recorded on the RPO label. "To be honestly frank about it, these are not pieces that the great international companies are up to doing at the moment," says Previn.

"It is a great point of pride," Previn continues. "To the best of my knowledge, we're the only major orchestra in the world that does this. We all contribute our services, and we all reap, if there are any benefits to be reaped. It's a different atmosphere, we're doing it for ourselves. It's a very good thing."

And under Previn and Ashkenazy, along with RPO President Sir Yehudi Menuhin, the orchestra has increased its international touring.

"I've always felt that if there's a very great orchestra, it's very wrong to keep it parochial," says Previn. "I think it's undeniably of prime importance to the city in which the orchestra is found and its supporters can be proud of it. But when it reaches the stage where it is a world-class orchestra it means exactly that. As far as I'm concerned, it is the best export product any city has to offer."

CAPTION:Andre Previn conducting the Royal Philharmonic Orchestra.