ANYONE WHO has bought a pair of tickets for a first-run Broadway show of late knows all too well that, at today's prices, two on the aisle can mean one in the red. Seats for "Amadeus," "The Little Foxes" and "Women or the Year" are going for $30 apiece. But veteran theater-goers in New York and Boston also know that there are ways to purchase many of these good seats at half-price on the day of the performance.Guess where this sort of arrangement will be offered next?

Try centerstage, right in the heart of our town near Metro Center -- where the Cultural Alliance of Greater Washington is planning to sponsor a half-price ticket booth for the performing arts. In addition to this discount for same-day attraction, the booth will also sell full-price tickets for later performances. With support from the Greater Washington Board of Trade and many member corporations, the booth dubbed "TICKETplace" -- is to open in October at the beginning of the new performing arts season.

The idea behind the project is more than just a promotion. While the play's the thing, a full house keeps the thing going -- and more than a million tickets have been going unsold each year in Washington. With this theatrical version of the airlines' standby system, hopes are that houses will fill as more people are able to afford evenings at the National, the Kennedy Center, Arena Stage and other theaters and concert halls here.

Don't expect this to bring regular prices tumbling down to good-old-days levels. Still, if the experiment is a hit, the additional revenue generated could help to offset the heavy costs of presenting top-flight entertaniment.