It was a special kind of trade show -- the Washington arts on exhibit with painting, miming, dancing, singing and acting performers showing off their wares last night in the great hall of the old Pension Building.

More than 80 member groups of the Cultural Alliance of Greater Washington joined to stage a "festive evening with the arts" as a fund-raiser for TICKETplace, the half-price ticket booth, which is scheduled to open Nov. l0.

When arts groups get together for a fund-raiser, they don't have to worry about entertainment. They can supply their own.

At the entrance of the Pension Building (now renamed the National Building Museum), the Paul Hill Chorale serenaded the more than 500 contributors who paid $25 to $100 for tickets to sample the arts of Washington as well as a buffet. On center stage, a Scottish country dance group was having a fling while two performers were doing a mime show on the main floor.

The exhibit booths also reflected the diversity and liveliness of the Washington arts scene. Alongside displays from the larger institutions like Wolf Trap and the Kennedy Center were exhibits of the programs of such groups as the Woolly Mammmoth Theatre Company, the Thomas Circle Singers, the Glen Echo Dance Theatre and the Alexandria Community Singers.

Mayor Marion Barry brought the news that he hopes to add more funds for the arts in the city's 1983 budget.

"You judge the character of your city by its culture," Barry emphasized.

TICKETplace, patterned after the successful operation in New York, will offer half-price tickets for the day of the show for more than 50 performing arts groups in the Washington area. It will be located on the F Street plaza between 12th and 13th streets NW.

Each patron, while waiting in line, will be given a schedule of the day's events, explained Candace Johnson, wife of Luxembourg Ambassador Adrien Meisch and chairman of last night's festival of the arts.

"Perhaps someone who can't get a ticket to a hit show at a larger theater will discover a program at a small theater," Johnson said.