The Prince George's County Council, faced in an election year with having to choose between two Metro routes into the southern part of the county, voted 6 to 5 yesterday to build both of them.

The council, in a formal request to a regional task force restudying Metro, asked that subway lines be constructed to both Rosecroft Raceway and Branch Avenue, the two terminals that had been in compttition.

The vote comes just one week before the regional task force restudying Metro is to decide what one system of Metro routes to recommend to the federal government for completion and financing. At no time the 17-month restudy has a double rote to the southern part of the county been analyzed, and the new proposal could add time, difficulty and money to both the study and the ultimate cost of completing Metro itself.

Council member Francis B. Francois, who is also chirman of the regional task force, told council colleagues yesterday that their action was "irresponsible."

"We raised the most hell about the costs of Metro," Francois said. "And in one motion we add $175 million. If this weren't 1978 and the election weren't coming up, this motion wouldn't be on the floor."

Primary elections for the council are scheduled in September. And many council members will be seeking reelection. The Rosecroft-Branch Avenue question has been hotly debated in the county and both terminals have strong support from citizens who are among the most poorly served by public transportation in the metropolitan area.

The Branch Avenue terminal would be just inside the beltway and east of Branch Avenue. The Rosecroft terminal would be outside the beltway near the racetrack and Brinkley Road. It had been assumed that the council would choose either one place or the other.

But Frank Derro, director of the country's Department of Transportation and Public Works, suggested a Y-type routing yesterday that would serve both areas.

The line would come from the Anacostia station at 14th Street and Good Hope Road SE in the District via St. Elizabeths Hospital, then generally parallel Wheeler Road to the Prince George's County line at Southern Avenue.

Somewhere in the Wheeler-Southern area, one branch of the line would run east to the Suitland Federal Center area then south to the Branch Avenue terminal. The other branch would head generally south from Wheeler and Southern to Rosecroft, with one station located somewhere along Wheeler Road. A once-proposed station at St. Barnabas Road would not be built. Neighbourhood opposition, centered around protecting a historic church there, has been strong.

The $175 million additional cost was Derro's best estimate. No estimates have been made of potential ridership and operating expenses two other factors that are critical in the regional restudy to all of the various Metro systems being discussed.

After the regional task force takes its final vote on recommendations, the Metro staff and local jurisdictions must then develop a plan to pay for both constructing and operating a completed Metro system. The federal Department of Transportation has withheld Metro construction money until the restudy and the financial plan are completed. Aug. 31 is the mutually agreed upon deadline for both exercises.

Francois, in an interview later, said that the regional body could reject the proposal and sent it back to the county, decide itself what to do in Prince George's, or permit further study.