In response to a National League Expansion Committee questionnaire, Capital Baseball, the group of investors seeking a baseball expansion franchise for Northern Virginia, will submit an answer today that includes a proposal for a massive sports complex near Dulles Airport, the group's organizer, Bart Fisher, said yesterday.

If awarded one of the two teams that will begin play in 1993, Fisher said his group will privately finance a 315-acre facility that would be located on Route 606, not far from where it intersects Route 50, just west of Dulles.

The complex would include a 50,219-seat baseball stadium, a football stadium if Washington Redskins owner Jack Kent Cooke chooses to move his team to the site, a 320,000-square foot exhibition hall that would accommodate 10,000 seats, a 500-room hotel, a multipurpose plaza and parking for 20,250 cars, Fisher said.

Fisher said he has spoken to Cooke's organization this week, although the project is not contingent on the football stadium. Cooke, whose team's lease for RFK Stadium expires at the end of this season, said "my organization is constantly canvassing every bit of information concerning stadiums and everything having to do with sports."

Negotiations between Cooke and the D.C. Armory Board about a new stadium that would keep the Redskins in the District have taken a more positive turn recently, a source familiar with the negotiations said Wednesday.