A stopgap plan for continued financing of Metro construction has been revived, and agreement has been reached on a study of the future construction program that could lead to a shortening of the long-planned Mid-City line in the District of Columbia.

If, as Metro officials now predict, the seven other affected local governments in the region ratify the financing plan, work can be extended without interruption on six rail routes totaling 60 miles from downtown Washington into the Maryland and Virginia suburbs.

The dispute had threatened to halt the award of further contracts on the rail system.

The impending and almost-certain agreement on stopgap financing is one of six recent actions that are expected to affect the extent and shape of the projected 100-mile rail system.

The original 4.6-mile route already in operation was extended a half mile Monday, when service on the downtown end of the line was extended from the Farragut North station to Dupont Circle station at Connecticut Avenue and Q Street NW.

Although the Fairfax City lawsuit attacking Metro's stopgag financing plan is still alive and scheduled for a hearing Feb. 1, the Metro board voted to eliminate a clause from the plan that formed a major basis of the city's complaint. The clause was interpreted as meaning that only a 60-mile rail system would ever be build, and that the Vienna line, which would serve Fairfax City, would be eliminated.

Following Metro's action, the Fairfax County Board of Supervisors voted unanimously Jan. 10 to approve the stopgap plan. After a meeting two days later with transit officials, Mayor Harold L. Miller of Falls Church - the last holdout - predicted that the City Council will approve the plan next Monday.

That would permit Metro to ask the U.S. Department of Transportation to begin releasing funds to continue work.

The stopgap plan is intended to stretch available and potential funds - a total of $942.8 million - to finish building and start operating the 60 miles of routes while the fate of the officially adopted 100-mile system is being determined politically.

The 60 miles would include routes from downtown to Shady Grove, Silver Spring, New Carrollton and Addison Road stations in Maryland and the Huntington and Glebe Road stations in Virginia.

Structural work on all or part of these lines already is under way. The new funding would permit the finishing of stations and the installation of rails and other equipment to permit the routes to begin operation.

Much of the other unbuilt mileage is being subjected to a study, mandated by Congress and the U.S. Transportation Department, to see if cheaper forms of transit could be substituted. That study is being overseen by a joint committee of the Metro board and two units of the Metropolitan Washington Council of Governments.

In other matters related to Metro:

Robert E. Patricelli, mass transit administrator for the Transportation Department, told the joint study committee that the subway route from Silver Spring to Glenmont can be exempted fromthe study. But he reminded the comittee that the federally imposed ceiling $4.7 billion for the full Metro system still stands - which means that construction of the Glenmont line could lead to elimination of Metro routes elsewhere on the Metro system.

The committee agreed to add the Greenbelt route in prince George's County to the study of possible cutbacks.As part of the agreement, the District of Columbia agreed to consider cutting back that line within the city - the so-called Mid-City line - at some point short of the Fort Totten station, which would be the last one before trains enter Prince George's. Possible points of cutback might be the Columbia Heights station at 14th and Irving Streets NW or at Georgia and New Hampshire Avenues NW.