Innovative spirit of London theater steals the spotlight

London theater is no longer looking to New York for inspiration: The trend increasingly is the other way around. Why?

Observers here point to a new spirit of theatrical innovation in the British capital - a willingness to take the kind of risks the theater needs if it is to move beyond the well-worn formulas of the past.

And although the results are mixed dramatically, the message is plain: Audiences love it and theater professionals are intrigued. Attendance is clearly on the upswing in London despite the dampening influences of television and economic hard times. And this new mood of innovation has generated enough excitement to make many Broadway impresarios sit up and take notice.

And what are they noticing? Two significant developments:

* An emphasis on musicals. Nearly one-third of this season's West End shows fall into that category, and for two important reasons: artistic interest on the one hand, hard economics on the other. Apart from many British directors' growing fascination with the mode from a purely creative standpoint, theater companies here are increasingly looking to a winning musical as the only kind of spectacle that has a strong potential to outdo television.

This idea was largely generated by the recent spectacular hits of English composer Andrew Lloyd Webber (''Evita,'' ''Joseph and His Technicolor Dreamcoat, '' ''Cats'').

Not long ago even the Royal Shakespeare Company (RSC), world-renowned for its classical works, decided to test the theory for itself by mounting ''Poppy,'' its first musical in some time. Despite mixed reviews, it has become a box office hit.

* Boldness in presentation. In two current productions - ''Daisy Pulls It Off'' and ''Jean Seberg'' - British playwrights, directors, and producers took plays that were not sure favorites and made them into hits.

''Daisy Pulls It Off'' - though winner of the coveted Society of West End Theatres award for best comedy of the year - might well have been doomed to obscurity had not Andrew Lloyd Webber seen it performed outside of London awhile back. Enthralled by its unaffected charm, he decided to produce it himself and take it to the heart of theaterland.

It was a gamble: The play lacks the glitter and gloss of a sure bet. But it is a simple tale, well told, and with its clever staging, crisp acting, and intelligent style, ''Daisy'' has indeed pulled it off.

But without a doubt the biggest talking point of the current London theater season has been the musical drama ''Jean Seberg.'' Playing at London's prestigious National Theatre, it has probably generated more controversy than any other West End production in recent times.

The initial rumblings started long before the play had even opened. Directed by the National Theatre's chief artist, Sir Peter Hall, the other heads behind the production are all American: composer Marvin Hamlisch, lyricist Christopher Adler, and dramatist Julian Barry. Some British critics argued that a nationally subsidized theater such as the National should not be used as a less costly testing ground for what is obviously Broadway bound. (While ''Jean Seberg'' may transfer to Broadway later this year, that has yet to be confirmed.)

Others maintained that Anglo-American collaborations are the way theater should be moving - that British dramatic subtlety and control coupled with the American flair for effect could, with the right handling, be a winning combination. If such proves to be the case, everyone benefits.

When ''Jean Seberg'' opened, the main point of contention shifted to the play's subject: Jean Seberg was the small-town girl from Iowa who shot to stardom in the late 1950s - the vehicle for her meteoric rise being ''Saint Joan ,'' Otto Preminger's epic film about the life of Joan of Arc.

The film failed. But Miss Seberg had captured the imagination of the media, so the starmaking machine ground on - for a while. She made more films, most of them disasters. Then she went off to Paris to begin her career anew; that too failed.

In 1979, after several nervous breakdowns, Jean Seberg resurfaced on a Paris side street after nearly a decade of obscurity: She was found dead from an overdose of pills.

Not the obvious material for a toe-tapping musical. But that isn't the fundamental problem with this production. In fact, its earnest attempt to expand musicals as an art form deserves high praise. The few truly inspired moments of the evening do support the notion that a musical approach can, given the right story, heighten the dramatic appeal of a profoundly serious subject.

But Jean Seberg isn't that subject. She simply does not epitomize the American Dream made rotten by the worms within: This was no noble heroine. To attempt drawing a parallel between her own life and that of Joan of Arc, as the play blatantly does, is its undoing. To do so is to exploit the selfsame methods of media hype that this Seberg saga is trying to condemn.

Of all the epitaphs the play offers following her death, Otto Preminger's best sums up the moral of the story: ''Jean Seberg had a sudden flush of success and it went away. Some people survive it. Others don't.'