Mayor Marion Barry, under Congressional orders to come up with a way to eliminate the District of Columbia's $296 million long-term debt, yesterday proposed a three-part plan that would require the federal government to pay $100 million of the costs.

Under Barry's proposal, both the city and federal government would each pay off $100 million of the debt over the next ten years, while the remaining amount would be financed by municipal bonds issued by the city.

"The accumulated deficit condition itself came about. . . through decades of federal financial management and budgetary decisions," Barry said in a letter to Sen. Arlen Specter (R-Pa.), chairman of the Senate Appropriations Subcommittee on the District of Columbia.

Congress has been cool to previous city requests that the federal government pay part of the debt. An earlier Barry plan to pay off the entire debt by issuing municipal bonds failed to gain the approval of Congress.

Despite the rejections, Barry said in his letter, his new plan was "an equitable special partnership between the federal government and the District."

"It was my administration that identified the problems posed by the accumulated general fund deficit and that proposed appropriate suolutions to it," said Barry.

The mayor's letter recounted the city's first-time-ever audits of its finances and balanced budgets for the past two fiscal years. He also pointed out that the city and federal government shared the $38 million cost of setting up the city's financial management system and are cooperating in efforts to finance city employe pension programs.

Under Barry's plan, the federal government would match the city's payment on the deficit for a maximum of $20 million each year.

Barry's proposal, which was due in Congress last Friday, was not released publicly until late yesterday.

Congressional officials, who control the city's budget, could not be reached for comment yesterday.