The Metro Board, hoping to close out a long and bitter controversy over the route of the proposed Green Line in southern Prince George's County, yesterday unanimously reaffirmed plans to build the line to Rosecroft, not Branch Avenue.

The board hopes its decision will lead a federal judge to lift an injunction he imposed last March halting all work on the Green Line's southern portion.

But supporters of Branch Avenue, the route shown on Metro's original 1968 master plan, charged that the decision was financially unsound and politically motivated and said they would try to block it in court. About 15 occasionally noisy backers of that original route sat in the meeting room yesterday displaying signs urging its retention.

Judge Norman Ramsey of the U.S. District Court in Baltimore, ruling on a suit filed by Branch Avenue advocates, had earlier found that Metro made technical errors in advertisements for hearings on its proposed shift to Rosecroft, a route change the Prince George's County Council favored.

In March, Ramsey ordered Metro to stop construction pending new public hearings and a complete rethinking of the alignment. That reevaluation was concluded yesterday with the board upholding its decision for Rosecroft.

Metro must now return to Judge Ramsey and ask that he lift the injunction.

Yesterday, Frank Haskell, an attorney representing the Branch Avenue supporters who filed the suit, said his side would argue for keeping the injunction in force on the grounds the court has not addressed other points in the suit.

Just before the vote, Prince George's County Metro Board member David Hartlove, who also sits on the County Council, spoke in favor of Rosecroft. He said it would be cheaper to build, would have higher ridership and would spawn more commercial development.

Proponents of Branch Avenue concede building there would be more expensive. But they point out that construction costs are covered almost in full by state and federal funds. They maintain Branch Avenue would attract more riders, as well as serving existing employment centers better and costing the county less in operating subsidies.

Branch Avenue supporter Sue Mills, who defeated Hartlove for his council seat, said yesterday that the Metro Board's vote should have been delayed until she and other new council members take office Dec. 6.

Metro often follows the wishes of local jurisdictions in deciding route questions. Mills, calling the November election a referendum in which the county rejected Rosecroft, said the newly constituted council would back Branch Avenue if it had an opportunity to vote.

Mills said that six of the new council's nine members -- herself, Floyd Wilson, Hilda Pemberton, JoAnn Bell, Anthony Cicoria and James Herl -- would support Branch.

However, calls by reporters indicated that Wilson would not support such a change and that Pemberton and Herl were undecided. "I have an open mind on the matter; both lines have merit," Herl said. Other members could not be contacted.

Hartlove defended the timing of the Metro Board's action. Building to Rosecroft is a sound move, he said, and the new members have "no information, no knowledge of what's been going on . . . . The old council has been working on it for over seven years."

Mills said she feared that the decision will touch off a new round of legal battling that will assure no line is built in southern Prince George's County. The federal government is cutting back on rail funds and many people fear it may eventually cancel the route.

Current schedules have the line going into service in the early 1990s as the final segment of Metro's full 101-mile system. Construction costs are estimated at between $680 and $800 million in so-called January 1985 dollars, a calculation that reflects the value the currency is expected to have that month.

Yesterday's vote also reaffirmed an earlier decision by Metro to shift the D.C. portion of the southern Green Line to an alignment farther south from that in the 1968 plan.

D.C. officials welcomed the vote, hoping that it would allow long-delayed construction to resume. When the injunction was imposed, Metro was seeking a contractor for a $60-million tunnel under the Anacostia River, the first major work on the line in years.

Getting construction moving on the so-called inner city Green Line between Anacostia and U Street is a major objective of the administration of D.C. Mayor Marion Barry. It is supposed to open in the late 1980s.

During yesterday's meeting, Metro general counsel John Kennedy told board members that the final decision on the routing lies by law with them. However, opponents could block it by pressing their lawsuits and filing new ones. The County Council, if it chose, could raise obstacles by appointing a new member to the Metro Board and blocking funds. Washington Post staff writer Michel McQueen also contributed to this story.