The Reagan administration has proposed spending $250 million in federal funds for expansion of the Metro subway system next year, an appropriation in line with the transit authority's requests, a federal source said yesterday.

Under a proposal drawn up by the Office of Management and Budget, the Metro system would likely be one of the few transit systems in the United States to avoid major cuts in construction funds, officials said.

The administration is considering severe cutbacks in spending for mass transit as part of a plan to reduce the federal deficit. Sources said that Metro's construction grants would be "virtually untouched" because the rail system has been financed under a special congressional authorization.

Other federal officials said they expect the proposed Metro allocation to undergo futher review. But they described $250 million as a "reasonable payout" next year under the congressional authorization.

Other forms of federal aid normally provided to Metro might be reduced under the administration's proposals, officials said. The transit agency plans to obtain $57.8 million in federal grants next year under existing aid formulas to buy buses, build garages, purchase rail equipment and help subsidize operating costs.

These sources of federal funds might be eliminated under the administration's current proposals, officials said. However, the proposed cutbacks appear likely, however, to face opposition in Congress.

Metro officials said they had not received the administration's proposals and were not prepared to comment on them. Nevertheless, they said the transit agency's current plans call for about $250 million annually in federal construction funds during the next four years.

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