The 35,000 motorists who daily use the George Washington Memorial Parkway in Virginia can expect rushhour delays of an hour or more beginning in April when construction workers start resurfacing the five parkway bridges between Rosslyn and Chain Bridge Road (Rte. 123).

At the same time, traffic will be slowed on Canal Road in the District, when the city begins resurfacing that popular two-lane commuter route between Chain Bridge and Georgetown. The project is expected to begin in July and take about a year. Plans to redeck Chain Bridge this fall have been postponed a year because a good portion of the G.W. Parkway traffic is expected to use the bridge and Canal Road.

The $3.7 million resurfacing project will require that one lane of the fourlane parkway be closed for up to 18 months, according to parkway Superintendent Don H. Castleberry. But extensive traffic delays are only expected for about the first three months, mainly in the morning for inbound Washington traffic.

All buses and trucks -- including commuter, government shuttle and Dulles Airport buses and U.S. mail trucks -- will be prohibited in that north section of the parkway during the entire construction period because the vehicles will be too wide for the narrowed lanes, Castleberry said.

Canal Road will continue to be two lanes during rush hours. The road between Georgetown and Arizona Avenue will be one-way during non-rush hours -- which way is not yet determined -- because of the construction, according to James Spellman, assistant director of the city's highway construction division.

Details on the construction projects and accompanying traffic restrictions will be released by the federal and District highway departments in the next month or two.

The five parkway bridges are being redecked at the same time to shorten the construction period, Castleberry said. In addition, the Federal Highway Administration is calling for double-shift construction on the bridges, which will shorten the normal 2 1/2-year construction period by at least one year. The contracts are actually expected to allow 24-hour-a-day construction, but strict Arlington County noise regulations preclude most construction work between 10 p.m. and 6 a.m.

The major parkway delays will affect Washington-bound traffic in the morning when construction closes one of the two lanes on southbound Spout Run Bridge. Since the other bridges are four lane, only one lane will be closed at a time. That will leave three lanes open, including two for rush-hour traffic. The work on Spout Run Bridge is expected to be done by July.

The deterioration of the 20-year-old parkway bridges has been hastened by winter use of salt to melt ice and snow, according to Park Service engineer George Walvoort. The salt seeps through the bridge concrete, corroding its steel reinforcements.

The Park Service redecked two parkway bridges north of Rte. 123, over Dead Run in 1974 and Turkey Run in 1976, and did major repair work on Pimmit Run Bridge in 1977, projects which kept the parkway in an almost constant state of repair and convinced the Park Service to do the remaining bridges all at once.

Two year ago, the District redecked four of its major bridges and soon will have to redeck the westbound 14th Street Bridge, East Capitol Street and Michigan Avenue Bridges as well as Chain Bridge, according to Spellman.