San Francisco hotel workers reached a tentative three-year agreement with five major city hotels, but a union spokesman promised walkouts Friday at hotels where negotiations have stalled. Local 2 of the Hotel and Restaurant Employees Union reached accord with the Hilton, the Fairmont, the Mark Hopkins and two Sheraton hotels. There is no all-inclusive hotel employers association in San Francisco and negotiations are continuing with other hotels. The issues involve wages, benefits and working conditions. The union represents maids, stewards, bellhops, waiters, dishwashers, bartenders and cooks.