PHRASES you can hear leaving the theater in Washington: "Maybe I should have bought a new shirt instead." "Twenty-five bucks for that?" "I'm tired of cabs, why don't we just walk the 19 blocks?"

Going to the theater can be a real gamble these days. With tickets selling in the neighborhood of $20 to $30, quiet evenings with "Remington Steele" look better all the time. If you crave the occasional taste of live theater, however, there are ways to see plays without busting the weekly budget. You can move to England where tickets are cheap. You can blend in with an audience during intermission and grab a vacant seat right before the second act. Or you can become part of the dramatic process -- as an usher.

That's the way I got to see three shows last weekend: "Twelfth Night" at the Source Warehouse Rep, "Passion Play" at Arena Stage's Kreeger Theater, and "The Beautiful Lady" at New Playwrights' Theater. If I had paid the full ticket price for each play, my weekend at the theater would have set me back $52.75. Because I was an usher, I saw those three fine shows for absolutely nothing and got a cup of coffee at New Playwrights' to boot. Nice deal.

Most theaters in Washington use volunteer ushers. Not only are they eager for help, many are downright desperate for ticket-takers, program-stuffers, seat-showers, etc. The schedules are flexible -- many ushers work one night during the run of each show -- and because you're a volunteer, you can quit with no regrets. (Paid ushers, on the other hand, enjoy neither the flexibility nor the carefree spirit of volunteers, but they like that extra jingle.)

My weekend started on Friday night with a trip to Arena for "Passion Play." I arrived at the theater one hour early, was issued a badge and flashlight, and joined the other ushers in stuffing programs until the house manager called us to attention. "Make sure people have tickets to the right theater," he said. "At intermission some of you must guard the stage; be careful that patrons with drinks don't reenter until they've finished." In closing, he added, "And remember, if you get a chance, drop a letter to our comrade who ushered 30 performances of 'Banjo Dancing.' She's in Room 318 at Sibley Hospital. Ha ha, just kidding." Time to move out and sit 'em down.

After madly chirping "Enjoy the show!" to anyone who would listen and showing about 35 people to their seats, I was free to watch "Passion Play." My only trepidation arose when it came time to seat patrons after the show had begun. For a moment I panicked under the pressure, but then with flashlight firmly in hand, I scowled at the late-comers and deposited them firmly in their seats. A star was born.

Ushering at the Source Theater's Warehouse Rep was even easier. The theater i general admission, so folks grab whichever seat catches their fancy. For half an hour I was left with the difficult tasks of grinning broadly, handing out programs and saying: "Welcome to the Source, enjoy the show." Another piece of cake -- another free show.

New Playwrights' Theater was the best deal. Ushers not only get to watch the show, they are also given an actual ticket for a seat (I had stood for the entire show at Arena and half the show at Source). Instead of showing people to their seats at New Playwrights', my duty was to tear tickets and send people into the theater with a reprise of my newfound mantra: "Thank you, enjoy the show." Like shooting fish in a barrel.

Don't get the idea that ushering people to their seats is a simple matter. Natural-born ushers like myself are few and far between. You'll find that the majority of crackerjack ushers in this town are made, not born. If, however, you think you have what it takes to join D.C.'s army of ushers, the following list should help. Oh yeah . . . enjoy the show. ON THE AISLES

Here are the names and contact numbers for theaters that use volunteer ushers:

ARENA STAGE -- Arena uses 45 ushers per performance, the Kreeger uses 29, the Old Vat Room uses 6 to 8. Call the house manager at 554-9066 after 8:30 p.m. There's a 500-person waiting list.

FOLGER THEATER -- Uses four ushers per performance. Call the box office at 546-4000 and leave a message for the house manager to get in touch with you.

HORIZON THEATER -- Uses 2 ushers per show. Call usher coordinator Amy Austin at 342-7706.

NEW PLAYWRIGHTS' THEATER -- Uses four ushers per performance. Call house manger David Perry at 232-4527.

ROUND HOUSE THEATER -- Uses four ushers per performance. Call 468- 4172 and ask for the volunteer coordinator. Information will be sent to you through the mail and an appointment will be set up.

SOURCE THEATER -- Number of ushers varies according to the show. Call house manager Michael Johnson at 462-1073.

STUDIO THEATER -- Uses two ushers per show. Call house manager Meggin Packman at 779-2686.

WOOLLY MAMMOTH THEATER -- Uses two ushers per show. Call production manager Nancy Turner at 393-3939. PLAY FOR PAY

Several theaters pay their ushers, but it's more difficult to hook on with them. Also remember that you have to be willing to work a regular schedule -- and sometimes see 20 performances of something like "Barnum."

FORD'S THEATER -- Uses 12 usher per show. Call house manager Daniel Zaic at 638-2941; there is a long waiting list.

KENNEDY CENTER -- The Concert Hall and the Opera House often use 25 ushers each; Eisenhower Theater uses 15; and the Terrace Theater around eight. Show up one hour before show time, ask for the head usher and make an appointment for an interview.

NATIONAL THEATER -- Uses 19 ushers per show. Call head usher Paula Minahan at 628-6161.

WARNER THEATER -- Uses 10 to 25 ushers per show. Call head usher Jim Horgan at 626-1050.