PITTSBURGH, FEB. 3 -- A tentative contract agreement was reached early today by United Steel Workers union negotiators and USX Corp.

The agreement came 30 minutes after a midnight strike deadline passed Saturday. Union President Lynn Williams explained the settlement to the union local presidents, but details were not immediately released. No formal vote was taken, union spokesman Gary Hubbard said.

Williams and USX Chairman Charles Corry had discussed by telephone a single detail 1 1/2 hours before the deadline, said John Reck, secretary to the union committee.

Both sides declined to discuss specifics of the negotiations, citing a news blackout. Union officials said previously they were seeking raises of about $2.30 an hour. Under the old contract, USX workers averaged $10.84 an hour, about $2 an hour less than workers at other major steel makers, Hubbard said.

The contract between the union and the nation's largest steelmaker was to have expired Thursday, but negotiators asked for a one-day contract extension that night and again Friday because progress was being made.

The contract covers 20,000 workers in Alabama, Illinois, Indiana, Minnesota, Michigan, Ohio and Pennsylvania.

The union has said USX's announcement Thursday that the company planned to create separate steel and energy stocks contributed to the union's decision to extend the talks.

Local presidents have said benefits, wages and protection for workers and retirees in case the steel division is sold were sticking points in the talks. As members of the union's bargaining committee, the presidents can accept or reject a tentative contract.

The union has said it wanted USX to follow other major steel makers, including second-largest Bethlehem Steel Corp., in restoring wage concessions. USX Chairman Charles A. Corry has said matching the rest of the industry would be too costly.