The Metro board voted yesterday to include in its budget the extension of the Red Line subway from Dupont Circle north along Connecticut Avenue to Yuma Street NW next December, a half-year earlier than previously scheduled.

Metro officials estimated the early opening will add 5,500 new riders to the system -- residents in areas like Cleveland Park who now drive their cars downtown to work but who will be able to walk to one of three new stations at Woodley Park-Zoo, Cleveland Park and Van Ness-UDC. The Van Ness station is at Yuma Street NW.

Officials said the line can be opened early by using passenger cars now on reserve and without causing longer waits for trains anywhere on the existing 37-mile system.

They also said that opening the line early will produce a net saving of more than $40,000 because bus service in the Connecticut Avenue corridor will be sharply reduced and rail fares will be higher than bus fares. The opening will add 2.06 miles to the system.

Although a final vote will be taken June 25, Metro General Manager Richard S. Page said yesterday that the vote means it is "virtually certain" that the new line will open early. The later vote was scheduled to give suburban Maryland representatives on the board a chance to get final approval from officials in Montgomery and Prince George's counties, where there has been concern that an early opening might disrupt existing service.

Metro Board Chairman Joseph Alexander said yesterday that "we can't afford not to" open the line early. David G. Hartlove Jr., the Prince George's representative, said he "wouldn't have any doubt" the line will in fact be opened early, despite his concerns about service elsewhere.

Besides offering rapid transit to District residents who live near the three new stations, the extension is expected to benefit another 5,500 people who now ride buses downtown from points in the District and Montgomery County north of the Van Ness-UDC station.These riders are expected to begin switching to rail at that station. They will pay higher fares to do so, but will be forced into it by the sharp cutbacks in bus service.

Finally, about 3,000 people who live in the District south of the Van Ness-UDC stop and who now ride the bus to work are expected to switch to rail. Their fares will increase slightly.

Many fares, however, will increase more steeply. A Metro spokesperson gave these examples:

Passengers for downtown from zone one in Montgomery County (Silver Spring and Bethesda) now pay a $2.20 round-trip bus fare and will pay $2.90 when they begin the bus-rail switch.

Zone 2 passengers (Rockville, Gaithersburg) now pay $2.80 for their bus round trip and will pay $3.50 under the new system.

A District passenger from the Friendship Heights area now pays $1.20 for a bus round trip, and will pay $1.90 under the new system.

Under current plans, bus service in the Connecticut Avenue corridor will be reduced with elimination of the L1, L5, and L7 routes and reductions in L4 and L2 service. However, these changes have not been officially approved and will be the subject of public hearings during the next six months.

Yesterday's tentative decision took the form of including a line item on the early opening in the board's 1982 budget. The $315.3 million budget, which has approved yesterday, represented about a 15 percent increase over last year.

Approval of the budget came from the board voted at the last minute to cut an additional $2.3 million from earlier proposals. The cuts mean reductions in train sizes on weekends and cutbacks in energy expenditures, and in Metro staff salaries and in computer programming acitivities.

The tentative decision to open the Red Line section early reflected the board's desire to open any completed portion of the system as early as possible. As Chairman Alexander put it: "I don't see how the board can not agree to open a line like that when it's all ready." Construction work on the three stations is essentially complete, and workers are putting in the finishing touches.

Board member Cleatus E. Barnett of Montgomery County said "serious questions" have been raised by officials there about the early opening. The concern is that service at the other end of the Red Line in Silver Spring might be adversely affected by the action.

Barnett said "I could not make a forecast" that the early opening would in fact receive final board approval on June 25, but other board members said Barnett's vote alone would not be enough to kill the plan.

General Manager Page predicted last month that an early opening of the new segment would mean more crowded trains and longer waits between them because there are not enough cars to expand and maintain service on the existing part of the system. New cars, currently being manufactured in Italy, are not scheduled to begin arriving here until early next year.

But early this month Page sent the board's budget committee a plan that would expand the system by using four cars that are now used solely for revenue collection, and two other cars that were damaged in a testing program but that are being repaired. The revenue collection cars are now used only late at night, after the system has shut down.

By using these six cars and taking cars from trains on some runs on the Orange Line, Page's new estimate said, the Red Line could be extended early without causing delays on the rest of the system. The only impact would be some more crowded trains on the Orange Line, which now has "significantly lower passenger counts" than the other two lines.

Under Page's plan, two trains will be added to the Red Line. At the same time, another train will be added to the Blue Line. CAPTION:

Map, Locations of three new stations on the Red Line extension are shown on map. By Dave Cook -- The Washington Post