Mayor Gavin Newsom on Sunday asked labor leaders and the management of 14 hotels embroiled in a nearly month-old dispute to resume normal operations for at least 90 days while the two sides try to negotiate a new contract.

In a letter requesting a 90-day "cooling off" period, Newsom said the dispute has caused "significant disruption" to San Francisco residents and visitors, threatening to harm the city's economic recovery.

It represented Newsom's first formal attempt to broker the peace in an increasingly bitter battle pitting several of San Francisco's landmark hotels against thousands of housekeepers, bellmen, cooks and other employees represented by the union, Unite Here Local 2.

The trouble began Sept. 29 when unionized workers frustrated with stalled contract negotiations struck four San Francisco hotels. Ten other hotels subsequently locked out their non-management workers. Labor leaders ended the strike of the four other hotels Oct. 13, but those workers also have been locked out.

The 14 downtown venues at the center of the conflict account for about a quarter of San Francisco's 32,500 hotel rooms, and include such luxurious properties as the Westin St. Francis, the Intercontinental Mark Hopkins and The Fairmont.

Newsom wants hotel management to end the lockout from Oct. 27 through Jan. 25, while labor leaders agree not to strike during that span. He asked for a response by Tuesday afternoon.

The hotels plan to respond by the deadline, said Cornell Fowler, a spokesman for the San Francisco Multi-Employer Group.

The union will eagerly agree to a cooling off period, said Mike Casey, president of Unite Local 2.

So far, the two sides have met three times with a federal mediator in an attempt to iron out differences over wages, employee health care costs and the main sticking point - the length of the new contract.

The employers are seeking a five-year contract, but local labor leaders want a two-year pact that expires in 2006 - the same time hotel labor agreements in New York, Chicago, Boston and other major cities will expire.