The sponsors of Ticketplace, the performing arts ticket booth planned for downtown Washinton, say they have raised about half the money they will need to go ahead with the project this year.

The Greater Washington Board of Trade has promised $50,000 and a group of corporations led by Xerox, The Washington Star, Warner Communications and the Shubert Foundation have offered another $50,000, according to Ticketplace's backers. These commitments were announced yesterday at a meeting of Washington arts and business executives called to drum up support for the plan. If still another $100,000 can be raised by early June, the Cultural Alliance of Greater Washington, which will operate the facility, means to try to have Ticketplace open by Oct. 1, the traditional beginning of the performing arts season.

"The bottom line is that arts organizations need to find new ways to increase their funding," said Stephen D. Harlan, president of the Cultural Alliance. Harlan defended Ticketplace's planned location on the F Street mall between 12th and 13th streets, after acknowledging that Farragut Square had been the group's first choice. The downtown site will draw more crowds on weekends and stands to benefit from a tremendous volume of commercial development under way in the immediate area, he said. In the next three or four years, 17 major building projects will be finished in the blocks surrounding Ticketplace, James Gibson, assistant city administrator for planning and development, told yesterday's gathering in the Corcoran Gallery auditorium.

Generally modeled on New York's TKTS and Boston's Bostix, Ticketplace will offer half-price, same-day tickets -- and full-price tickets for future dates -- to a variety of theater, dance and music events throughout the Washington area. The Kennedy Center, the National Theatre, Wolf Trap, Arena Stage, the Folger Theatre Group and Ford's Theatre are a few of the institutions that will participate. They will also help with Ticketplace's early cash flow, it was revealed yesterday, by pre-paying for advertising space on the outside walls of the booth.