The $4 million, 16-month bridge repair project on the George Washington Memorial Parkway in Virginia is set to begin May 1, the National Park Service announced this week.

Construction work on the five bridges between Spout Run Parkway and Chain Bridge Road (Rte. 123) is expected to cause rush-hour traffic delays of up to one hour for the 60,000 Virginia and Maryland motorists who use the four-lane parkway each day.

But the District Department of Transportation this week had some good news for motorists who use Canal Road across the Potomac, parallel to the parkway. The resurfacing of Canal Road, a year-long project planned to began in July, has been indefinitely delayed and may not start until the G.W. Parkway construction is completed in the summer of 1980.

"It's a boon for the many parkway motorists who will be shifting over to Canal Road," said park service spokesman George Berklacy. The city already had postponed construction work on Chain Bridge until after the parkway bridge repairs are completed. District officials had earlier predicted the Canal Road construction would not significantly add to traffic delays because no work would take place during rush hour.

The worst delays are expected on the G.W. Parkway during the first three months of construction, when inbound Spout Run Bridge ill be reduced from two lanes to one, according to Don Castleberry, superintendent of the parkway.

During the rest of the construction period, three lanes of traffic will be open on the entire length of the project during the day, with two lanes inbound from 6 a.m. to 2 p.m. and two lanes outbound from 2 to 10 p.m., Castleberry said.

At night, between 10 p.m. and 6 a.m., only one lane of the parkway will be open in each direction. This is because the bridge rapair contract, expected to be awarded this week, calls for nighttime construction as long as it does not violate Arlington County's 10 p.m. to 6 a.m. noise curfew.

All large buses and trucks will be prohibited from using the section of the parkway being repaired because they cause 10 times more vibration than cars and could damage concrete while it is curing, and because the parkway lanes will be only 81/2 feet wide through the construction areas, Castleberry said.

Few trucks use the parkway and those only under special permit. But some 200 buses a day will have to be rerouted, including buses to Washington from Dulles International Airport and Reston, he added.

The park service also has closed the parkway's three scenic overlooks and Fort Marcy picnic area during the work to permit storage of construction materials.

The park service decided to repair the five bridges simultaneously to shorten the construction time. Repair projects on three other parkway bridges west of Chain Bridge Road have delayed traffic for much of the past three years. The 25-year old bridges, like most area bridges, have suffered from winter use of salt to melt ice and snow. The salt seeps through the concrete and corrodes the steel reinforcement.

In addition, the Federal Highway Administration has called for doubleshift work on the project to cut the normal 21/2-year consruction period nearly in half.

Castleberry said the park service originally hoped to delay the repair work until I-66 is completed in 1982. The bridges are in such bad shape, however, that some temporary repairs would have to be done and these would also cause delays, he added.

While traffic jams on the parkway are expected to be had, at least until August, Castleberry said they could be reduced significantly if commuters would car-pool. A recent park service traffic survey found that 69 percent of the commuters on the parkway drive alone, 23 percent of the cars have two occupants and only 8 percent could be classified as car pools, with three or more persons.

The park service has met with Arlington and District officials to coordinate the repair projects. Castleberry said no other major construction is planned in the area, except for I-66, during the bridge repair work.

The District postponed the Canal Road repaving because of contract and financial problems, not out of concern over increased traffic congestion, according to transportation department engineer Charles Stuart.