Local governments have agreed to fund a $1.5 billion capital plan for Metro that will buy rail cars and buses and pay for enough maintenance to "keep the system afloat" over the next six years, transit officials said yesterday.

The plan, expected to be ratified within a week by the District and counties served by Metro, is a "basic, bare-bones agreement," Metro Chief Executive Richard A. White said. "It is the absolute minimum we must do to keep this system afloat."

Known as Metro Matters, the plan calls for the purchase of 120 rail cars and an upgrade of power and signal systems that will enable Metro to operate eight-car trains. An eight-car train can carry 200 people more than a six-car train, which is the longest Metro now operates.

It also allows for the purchase of 185 buses to relieve crowding, the construction of a bus garage in Virginia, upgraded bus stops and better information for bus passengers, such as the sort of real-time arrival information that subway riders have enjoyed for years.

Metro Matters also includes the construction of a backup control center for rail operations, so the subway can continue operating if anything disastrous happens to the main control center in the basement of Metro's downtown headquarters.

Transit officials said they were relieved that taxpayers will fund the plan, but they cautioned that it will take years before daily riders notice improvement because of the time it takes to manufacture rail cars and buses. If rail cars are ordered this year, it will be 2008 before all of them are carrying passengers.

"In the meantime, we have to keep the system alive, and that's going to be a struggle," White told Metro directors yesterday. Metro's rail cars are breaking down nearly twice as often as they did three years ago, creating increasing delays across all lines when ridership is surging. Statistics for Metrobus also show more and more buses sidelined with mechanical problems.

The plan took seven months of complex negotiations between Metro and officials from the District, Virginia and Maryland. White warned that without a fast infusion of money for maintenance and new rail cars and buses, Metro would tumble into a "death spiral."

At $336 million, the District will pay the largest share of the plan. Gladys Mack, who represents the city on the Metro board, said the agreement comes at the expense of other urban needs. "We are doing it, we are committed to it, but it is a very difficult decision for the District, and we have to forgo other things that are important to us," she said.

Two of the jurisdictions, Arlington and Fairfax counties, intend to generate part or all of their share from a bond referendum that will come before voters Nov. 2. Officials from both counties said they were confident voters will approve the plans.

Local governments already subsidize Metro's operating costs, the daily price of running buses and trains. Until now, capital costs -- the purchase of rail cars and buses and the construction of stations and subway extensions -- have largely been funded by the federal government.

The Metro Matters plan assumes a significant level of federal funds that have yet to be appropriated by Congress. If the federal government does not approve the money, the local governments say they will either find the money elsewhere or scale back the program.

Yesterday, several local officials called on federal officials to make new investments in the 28-year-old transit system.

"There's a seat at the table that's empty," said D.C. Council member Jim Graham, who represents the city on the Metro board. "The federal government is a major stakeholder in the success of the Metro system. Without their support, I don't think this is going to be done."

Almost half the subway riders during peak hours are federal employees, and more than 50 federal agencies or work centers are located next to Metro stations.

Gerald E. Connolly (D), chairman of the Fairfax Board of Supervisors, said that justifies special consideration by the federal government. "This is not Whoo-Whoo, Wyoming," said Connolly, who appeared before the Metro board to voice his county's support for the capital plan. "This is the nation's capital. The federal government is the single biggest user of this system."

The Metro Matters plan will cover the transit system's basic needs for the next six years. "Before this agreement expires, we're going to need another one," White said. He and other Metro officials said they were eagerly awaiting the recommendations of a blue-ribbon panel that is studying Metro's financial structure and examining whether the region should establish a source of funds for Metro that is separate from subsidies paid by local governments from their general budgets.

Gerald E. Connolly, chairman of the Fairfax County board, said the federal government must pay, too.