Bridge repairs that are likely to create rush-hour traffic jams will begin tomorrow on Virginia's George Washington Memorial Parkway and Chain Bridge Road (Rte. 123).

The $6 million construction project, which will redeck five 20-year-old parkway bridges, will not be completed until the fall of 1980, but the most severe traffic problems caused by the work are expected to be over by August, according to spokesman for the National Park Service and the Federal Highway Administration.

Delays of up to one hour during morning rush hours are anticipated if most of the 30,000 motorists who daily use the parkway continue to use it during the construction period.

The major delays will occur during repair of Spout Run Bridge when the Spout Run and George Washington parkways, which each normally have two lanes of traffic during morning rush, will be reduced to one lane each.

During the 16-month construction period no buses will be allowed on the parkway and no more than three of the parkway's four lanes will be open in construction zones. During morning hours (6 a.m. to 2 p.m.), two lanes will be open inbound to Washington, and during evening hours (2 p.m. to 10 p.m.) two lanes will be open outbound. From 10 p.m. to 2 a.m., only one lane in each direction will be open.

The speed limit in the three-mile construction area will be reduced to 30 miles an hour from 50 miles an hour and no passing will be permitted. During rush hour, commuting motorists may choose either of the two open lanes but they will not be able to change lanes until out of the construction zone.