Metro should increase bus and subway fares sharply to control snowballing operating deficits and accept the losses in ridership that will result, an independent study of financial issues facing Washington area governments has recommended.

But the study, conducted by a 27-member commission sponsored by the Greater Washington Research Center, maintained that ridership losses need not be large. Increases that would drive 8 to 12 percent of Metro's riders into cars would shave about $100 million off the nearly $300 million in subsidy bills projected for fiscal 1986, it said.

Raising fares this way would reverse a years-old trend that has seen Metro grow more and more dependent on subsidies. The Metro board recently postponed a fare increase scheduled for January on the grounds that it would drive riders away and ultimately worsen the system's financial troubles.

The study gave no precise figures for what a particular bus or rail trip would cost under the proposed scheme. But in general, fares would have to go up about 40 to 60 percent faster than Metro's plan, which calls for fare increases roughly following the rate of inflation.

The impact of sharp fare increases on low-income people could be softened by sale of special cut-rate tickets, the study said. The study pointed to Arlington County, which has a program to buy Metro Flashpasses and resell them to qualifying families at a discount.

Under current policies, bills paid by local governments to keep the trains and buses running will rise from $113 million in fiscal 1982 to $287 million in 1987, a 155 percent increase, the report said. That will be the fastest growing single item in local governments' budgets, it said.

The study also called for higher gasoline taxes and parking fees in all jurisdictions to take care of highway maintenance and construction.

"The highway problem has not received the attention it deserves, in part because we've put so much effort on Metro," said former U.S. defense secretary Robert McNamara, who headed the study. Area officials believe that roads and bridges have suffered seriously from deferred maintenance.

Concerning Metro, the commission also recommended that:

* Long-term planning responsibility for transit should be turned over to the Council of Government's Transportation Planning Board. The current Metro board could be restructured as a management board to oversee operations, it said.

* Local governments should pay for rail construction based on what would be built within their borders in the next few years. Currently, payment is based on what a jurisdiction is meant to get under the full 101-mile system, which is not scheduled to be finished until the 1990s. That has caused jurisidictions like Prince George's County to have paid a disproportionate sum for the amount of service they now receive.

* The inner city Green Line between Columbia Heights and Anacostia should be built regardless of any future rethinking of unstarted portions of Metrorail.

* To assure service quality, Metro should not open the Blue Line between National Airport and Huntington and Yellow Line track between Gallery Place and the Pentagon until a sufficient number of new railcars is on hand. Some Virginia officials, impatient over delays in delivery of cars, have suggested spreading the existing fleet over more area to open the new track.