The Northern Virginia Transportation Commission has endorsed proposals to establish a commuter rail system serving outlying suburban areas and to start a state-subsidized taxi program serving Metro subway stations in Alexandria.

The proposed commuter rail system would provide rush-hour train service on two branches connecting Washington's Union Station with Fredericksburg and Manassas. Officials said prospects for the long-debated project are uncertain.

The experimental taxi program, expected to begin next month, will offer low-cost rides on weekday nights to-and-from the Braddock Road, King Street and Eisenhower Avenue stations. Fares would be based on special zones and would range from $1 to $4. The service is to be expanded to weekends.

In a resolution adopted Thursday night, the transportation commission said it "endorses the concept of commuter rail service" on the two proposed routes. The system, which would resemble Maryland's commuter rail service, is considered likely to help ease traffic congestion in the I-95 corridor.

A study last year by R.L. Banks & Associates Inc. found a commuter rail system to be "feasible," but described prospects as uncertain because of high costs and "lack of cohesive public initiative." The report was prepared for the Metropolitan Washington Council of Governments and the Virginia Department of Highways and Transportation.

The Northern Virginia commission later challenged the consultant's estimates. The commission's staff said the system could be set up at a cost of $6.8 million and would incur a $1.3 million deficit over two years. The consultant had put capital outlays at $46 million and annual losses at $2 million.

The commission, a regional coordinating agency, urged state and local officials to seek funds to finance the plan, which is expected to be reviewed by a state legislative subcommittee headed by Del. David G. Brickley (D-Prince William).

The proposal was criticized by Fairfax County Supervisor Joseph Alexander, a commission member, who termed it "marginal at best." Alexander asked the commission to consider establishing commuter bus lines in the I-95 and I-66 corridors to serve outlying areas.

The Alexandria taxi project is among several recent proposals aimed at reducing county and city transportation costs. Officials said the taxi service, which will be subsidized by a $100,000 grant from the Virginia highway agency, is expected to prove less costly than bus service.

The commission is considering a similar taxi project to serve the Ballston Metro station in Arlington County. The District is seeking a federal grant for low-cost taxi service near the Fort Totten rail station in Northeast Washington.