Budget-minded Americans planning to invade Great Britain this summer should seek out one of London's best and most lasting bargains -- its theaters. The price of a single orchestra seat at a top Broadway show will often fetch two excellent stalls seats at the best West End houses.

Here's a sample of what's being offered. Remember that most London theaters are closed on Sundays.

"Starlight Express" (Apollo Victoria Theatre). London's hottest theater ticket gets you a seat aboard Andrew Lloyd Webber's "Starlight Express," a multimillion-dollar song-and-dance extravaganza conducted entirely on roller skates. Directed by Trevor Nunn, who three years ago gave London and New York the celebrated theatrical event, "The Life and Adventures of Nicholas Nickleby," "Starlight Express" is equal parts roller derby (choreography), "The Road Warrior" (costumes) and "The Little Engine That Could" (story). Amazingly limber, musically adroit cast members assume the roles of train engines and other cars. The trains engage in a series of elimination races to determine a champion. The action takes place on a 1.4 million-pound -- that's a million-plus bucks under any exchange rate -- computer-directed, movable roller freeway that encircles the audience, ensuring an excellent view.

Composer Webber keeps pace with Arlene Phillips' breezy rollerwork with a mixed bag of catchy, highly derivative songs and ballads covering every imaginable musical angle -- gospel, pop, country, heavy metal and rhythm and blues.

Tickets for "Starlight Express" are very difficult to come by, especially for Friday and Saturday performances. However, the theater is taking reservations for performances through March 1986. Also, a limited number of tickets is usually available for the 3 p.m. Tuesday matinees. The Apollo Victoria Theatre takes credit-card bookings at 01-630-6262; box office, 01-828-8665; Monday through Saturday, 10 a.m. to 8 p.m. (Remember the five-hour time difference.)

"Pravda" (Olivier Theatre). For those who prefer more traditional theater, there's "Pravda -- A Fleet Street Comedy," a presentation of the celebrated repertory company of the National Theatre of Great Britain. "Pravda" stars Anthony Hopkins in an acting tour de force as Lambert Le Roux, a Rupert Murdoch-like publishing magnate who controls much of London's tabloid empire. The script is by Howard Brenton and David Hare, who also directs the performance.

"Wild Honey" (Lyttelton Theatre). The National Theatre's other working theater, the Lyttelton (a third, the Cottesloe, reopens in the fall), is presenting "Wild Honey," an early work by a then-24-year-old Anton Chekhov, in a translation by Michael Frayn. In pre-revolutionary Russia, a group of friends and relatives descends on the Voynitzev family estate to celebrate the passing of the long, dark winter. This rite of spring becomes an excuse for passions, pent up during the winter freeze, to flow like honey from the hive, sweet and unrestrained.

Heading the excellent ensemble cast is Ian McKellen, who portrayed the legendary writer and lover D.H. Lawrence in the film "Priest of Love." As the immature, philandering Platonov, McKellen spends most of his stage time arranging and following through on liaisons with a variety of female characters.

For National Theatre productions, box-office phone at 01-928-2252. Credit-card bookings at 01-928-5933. Recorded information concerning performances at 01-928-8126. Box office open from 10 a.m. to 8 p.m. Monday through Saturday.

"Breaking the Silence" (Mermaid Theatre). Stephen Poliakoff's "Breaking the Silence" was a sellout when it opened as a Royal Shakespeare Company attraction in October 1984 at The Pit, the company's 200-seat studio theater. Little wonder. "Breaking the Silence" has recently reopened at the roomier Mermaid Theatre to accommodate larger audiences.

The play concerns the members of a pampered, privileged Russian family, the Pesiakoffs, forced by the new social order of the 1917 Revolution to make drastic changes in their life style. During the course of their transformation, the members re-evaluate and, in some cases, discover their need for each other.

The title, "Breaking the Silence," has multiple meanings, not the least of which is patriarch Nikolai Pesiakoff's (played by Alan Howard) single-minded obsession with an invention that will put sound on film. Gemma Jones is his wife, Eugenia, and Jenny Agutter is the faithful family domestic, Polya.

Box-office phone at 01-236-5568. Credit-card bookings at 01-236-5568 or 01-741-9999. Box office open from 10 a.m. to 8 p.m. Monday through Saturday.

OTHER ATTRACTIONS: "Hamlet" (Barbican Theatre). With Roger Rees and Virginia McKenna. Credit cards at 01-638-8891 or 01-628-8795. (In repertory with "Richard III" and "Henry V.")

"Waste" (Lyric, Shaftesbury). With Judi Dench and Daniel Massey, a Royal Shakespeare Company production. Credit cards at 01-434-1050/1550. Ends July 27.

"The Corn Is Green" (Old Vic). With Deborah Kerr. Credit cards at 01-261-1821. Ends June 29.

"The Caine Mutiny Court-Martial" (Queen's Theatre). With Charlton Heston and Ben Cross, directed by Charlton Heston. Box office at 01-734-1166/7.

"Other Places" (Duchess). By Harold Pinter, with Colin Blakely and Dorothy Tutin. Credit cards at 01-836-8243 and 01-240-9648.

"Man of Two Worlds" (Westminster Theatre). With Ian Cullen. Box office at 01-834-0283/4.

"Dance of Death" (Riverside Studios). By August Strindberg, with Alan Bates. Credit cards at 01-379-6433. (Limited season.)

"Sweet Bird of Youth" (Theatre Royal, Haymarket). By Tennessee Williams, with Lauren Bacall, directed by Harold Pinter. Box office at 01-930-9832. Previews from June 26.


* Most theaters accept advance bookings through major credit cards, including VISA, American Express and Access (MasterCard in this country).

* Tickets can be booked via ticket agencies located throughout London or through your hotel, usually through the porter. The fee for such service is usually 20 percent of the ticket price. Check before booking.

* The SWET Ticket Booth located in Leicester Square sells tickets for selected productions at half price on the day of performance. The ticket booth opens at noon for matinees and is open from 2:30 to 6:30 p.m. for evening performances. There is a nominal service charge for each ticket.

* Some theaters hold a limited number of tickets, called day seats, for the day of performance. Check with the theater box office.

* You can save money by purchasing tickets for productions in preview.

GETTING THERE: London's public transportation system is marvelous. Most theaters, West End and fringes, are accessible by subway or bus. Ask directions at your hotel or phone the box office. Also, those reliable Austin taxis are everywhere, manned by courteous, sensible drivers who know the route to London's many theaters cold.

TIPS: Many theaters have restaurants, cafes and bars as part of the theater complex, offering meals and snacks before, during and, in some cases, after the performance. You can place an order before the show for intermission drinks. Your gin and tonic will be ready for you when everyone else is stampeding the bar. (But don't be surprised if you can't buy an alcoholic beverage during a matinee performance, even on Saturday. There are government restrictions on hours for drinking in public places.) Contrary to rumors, the English bartenders will serve iced drinks. You can expect to pay extra for your program at most theaters. The price is usually less than a dollar. The menu of intermission munchies usually consists of mints and assorted super-sweet candies and chocolates, cups of ice cream and fizzy soft drinks. These are served by attendants harnessed with serving trays. The English continue to be great fans of smoking, despite a concerted effort by the government to point out its dangers through advertisements. Though the theater managers seem to have a more enlightened attitude toward public smoking than those who run the movie houses (where every seat comes equipped with an ashtray), you might find it necessary -- indeed, life-saving, in the case of smaller theater lobbies -- to spend your intermission outside the theater.

* Gary H