The Metro transit system, in an attempt to ease traffic congestion, has endorsed a controversial proposal to expand the hours during which car-pool restrictions are imposed on I-66 inside the Capital Beltway.

Metro officials said some Metro buses now are delayed on I-66 because of tie-ups stemming from a congressionally mandated relaxation of car-pool rules that took effect last year.

The transit authority's views are considered significant because Metro is one of two local agencies that must be consulted by federal officials before any shift in car-pool rules takes place.

The other agency is the Transportation Planning Board, a regional coordinating body affiliated with the Metropolitan Washington Council of Governments. The planning board recommended a similar expansion in the restrictions last month.

Rep. Frank R. Wolf (R-Va.), who won congressional approval of the measure to relax the rules, has said he opposes the new proposal.

Under the proposal, the eastbound lanes of I-66 would be restricted to car pools with at least three persons from 6:30 to 9 a.m. The restriction now is in effect from 7 to 9 a.m.

The restriction would go into effect for westbound traffic either at 3:30 p.m. or 4 p.m. and would last until 6:30 p.m. It now is in effect from 4 to 6 p.m.

The congressional measure eased the rules to permit use of the road by car pools with three persons instead of four. The new proposal calls for retaining the three-person requirement until congestion becomes severe, probably in the early 1990s. The four-person rule then would be reinstituted.