The redecking of the Woodrow Wilson Bridge, which has tied up Capital Beltway traffic since late last year, will probably be completed by mid-September, about seven months ahead of schedule, Maryland highway officials said yesterday.

Crews expect to finish laying a new precast concrete deck on the bridge's three westbound lanes this weekend and then will begin paving an asphalt roadway over them. Work on these lanes will be completed by May 25 if weather remains favorable, acting district engineer Edward H. Meehan said.

Crews will then begin redecking the three eastbound lanes.

Until the bridge is finished, traffic will continue to be restricted to one lane in each direction from 8 p.m. to 6 a.m. every night except Sunday.

All six lanes will continue to be open during the day.

American Automobile Association spokesman Tom Crosby said engineers have never before attempted to redeck a bridge the size of the Woodrow Wilson while keeping it open for rush-hour traffic.

The contractor for the $24 million job, Cianbro Corp. had said it could lay only seven of the 25-ton deck slabs a night, but with practice found it could do as many as 20, Crosby said.

About 130,000 vehicles used the bridge daily before the redecking began, making it the most heavily traveled six-lane bridge in the country, Crosby said.

Construction officials estimate that 15 to 20 percent of the regular nightly users have switched to other routes.

Congress provided a special fund to finance the job because the 21-year-old bridge's deck deteriorated into a hazardous maze of potholes and crumbling pavement.

Engineers have said that traffic restrictions for safety purposes would have been necessary next winter if reconstruction had not begun this year.

Motorists can obtain information on changes in the bridge restrictions on an American Automobile Association hot line, 222-6200.