Area motorists soon will get relief from longstanding restrictions on the 14th Street and Chain bridges that cross the Potomac River. But several miles downstream, work to replace the deck of the busy Woodrow Wilson Bridge began last night and is expected to tie up traffic there on week nights until early 1984.

Workmen began cutting into the roadway of the bridge last night about 11 p.m., 1 1/2 hours after work was slated to begin. Although traffic backed up into Virginia for about a mile, police officials said there were no major problems and that traffic was moving slowly across the span.

Although work on the bridge normally will not occur on Saturday nights, Dick Dooley, project manager for Cianbro Corp., which is doing the redecking, said they do plan to close the bridge tonight.

By the afternoon rush hour Monday, work crews hope to have put final touches on a $13.5 million renovation of 14th Street SW leading to the 14th Street bridge and plan to lift restrictions imposed there 2 1/2 years ago.

Chain Bridge, meanwhile, is set to receive full traffic again on Dec. 11, a week from today, ending lengthy detours thousands of drivers now must take. Only one of its three lanes is now open, as contractors finish a redecking job begun in June 1981.

The three bridge projects reflect lawmakers' commitment to raise spending on area bridges and highways, which are badly scarred by broken pavement and rust after years of neglect. If money is available, Key Bridge, Memorial Bridge, Roosevelt Bridge and parts of the 14th Street bridge itself are likely to get major renovation in coming years.

On an average day, more than 100,000 vehicles use the Wilson bridge, which opened in 1961 and is now part of Interstate 95. The $24 million redecking job, scheduled to take more than a year to complete, will be paid for with funds specially provided by Congress.

Plans call for traffic to be limited to one lane each way from 8 p.m. to 6 a.m. Monday through Thursday nights. On Friday nights, lane closures will last from 9:30 p.m. to 7:30 a.m. All lanes will be open Saturday and Sunday nights, unless work falls behind schedule.

The American Automobile Association predicts that two-hour delays will be common at night and has established a hotline -- AAA-6200 -- to give motorists the latest information on closures.

At Chain Bridge, located at a site where bridges have spanned the Potomac since the late 18th century, workers have put in a new deck, built a pedestrian ramp to the C&O Canal towpath below, eliminated a sidewalk to make the lanes a bit wider, and installed new safety barriers. The job cost $4 million.

Currently, only one of three lanes is open on Chain Bridge, the District's northernmost Potomac span. That lane carries inbound traffic in the morning and outbound in the evening. The D.C. government, which owns the bridge, plans to lift the restrictions next Saturday afternoon. From then on, traffic will move as follows:

Two lanes will be used by inbound vehicles and one by outbound between 6:30 a.m. and 10 a.m. on workdays. At all other times, the configuration will be two lanes outbound and one inbound. Between Arizona Avenue and Foxhall Road, Canal Road will be one-way inbound from 6:30 a.m. to 10 a.m. on workdays. It will carry only outbound traffic 4 p.m. to 7 p.m.

The six-lane expressway that carries 14th Street traffic onto the Potomac bridges has been restricted since work began in August 1980. Before that, it carried more than 50,000 vehicles on an average weekday.

In a 2,500-foot segment between C Street SW and the Jefferson Memorial, contractors have torn up and replaced heavily patched roadway dating to the 1940s. Care was taken in the job to waterproof the road's new concrete foundations, to prevent corrosion of the reinforcing steel inside.

Currently, three lanes are open and carry only outbound vehicles from about 3 to 7 p.m., and only inbound traffic at all other times. Crews are now painting the road stripes and moving signs, and hope to remove the traffic barriers by the afternoon rush hour on Monday. After that, there will be no restrictions.

The 14th Street bridge will not be clear for long, however. Next year, D.C. officials hope to begin redecking the George Mason Memorial Bridge, the span that carries non-express traffic to Virginia. Officials may divert the traffic onto the adjacent bridge now reserved for buses and carpools.