Is there night life south of Pennsylvania Avenue?

Tony Greco, proprietor of the Rive Gauche, and four generations of the Greco clan, are betting some $250,000 that there can be - beyond the odd student from George Washington University and staff members from the various branches of the Executive Department who gelost after dark in the tangled streets north of Foggy Bottom.

Thursday in the new Federal Home Loan Bank Board Building, just across 17th Street from the Old Executive Office Building, the Grecos held a VIP and media party to open "The Buck Stops Here," a new establishment which will be a cafeteria by day, a happy-hour bar in the twilight and a modified disco in the later evening. It is part of a new experiment, authorized by law last year, under which the government will lease space to private enterprise in government buildings, and the Grecos are hoping it will give the neighborhood a new character.

"This is the first time I've been in this neighborhood since the Nixon administration," said one of the VIP-media guests, Victor Lasky, author of the best-selling "It Didn't Start with Watergate."

"This new group in the White House doesn't invite me, and I don't blame them."