Transportation Secretary Brock Adams offered substantial federal help yesterday to [WORD ILLEGIBLE] subway's growing [WORD ILLEGIBLE] but [WORD ILLEGIBLE] indicate that the price would be a more active federal role in local transit decisions.

In a letter obtained late yesterday, Adams told top regional officials that he is willing to offer federal money on a stopgap basis to meet one pressing need and thus buy time to solve others.

However, it is clear from the letter that Adams expects more federal participation in a current study of unbuilt subway lines, that he wants another unbuilt line added to the study, and that he expects a long-term solution to Metro's construction and financial difficulties.

Adams' letter is the first serious indication that the Carter administration is interested in taking a hand in Metro problems, comes at a time when there are growing pressures on local politicans to reduce Metro's burden on area property taxes. The total operating deficit for the next fiscal year for both bus and subway is projected at $76 million.

But of even more concern to both the federal government and local officials are the interest payments for $1 billion in revenue bonds that were sold to pay for Metro construction. The federal government guaranteed the bonds, and thus is liable if Metro defaults. At the time the bonds were sold, it was expected that revenues generated by the subway system would pay the interest, and ultimately, the principal.

Alexandria and Prince George's County have both taken positions against paying any of the revenue bond interest. A $12 million payment is due this year, and the figure rises to a total of $36 million next year.

Metro officials have been trying to get federal assistance for 80 per cent of the interest. That percentage represents the amount of money the federal government contributes to subway building projects today.

Adams offered in his letter to pay 80 per cent of the next fiscal year's interest - or $29.3 million of the $36 million. But a Metro payment "would cover the $12 million due on July 1," Adams, said.

That approach, Adams said, will permit "involved parties to better address long-term transit capital and operating financing issues without the burden" of the bond interest payments.

Last year, the Department of Transpotation financed a restudy of the Metro subway lines beyond the 60 miles that are either under construction under contract. That restudy is called the "alternative analysis," and the purpose is to decide whether subway or trolley, or bus, or highway or nithing might better serve the transportation needs of the affected areas.

One line - from Silver Spring to Glenmont - was excluded from the alternatives analysis, primarily at the insistence of Montgomery County Executive James Gleason. The line, estimated to cost between $270 million and $275 million, is the most expensive suburban segment in the planned system, It would be underground all the way north from Silver Spring up Georgia Avenue and 16th Street to Glenmont.

Yesterday, Adams requested that the Glenmont line be put back in the restudy. "The potential for either a different location for the line or an alternate type of service . . . should be closely examined," Adams said.

In his letter he offered federal funding to restudy the Glenmont line,i and also designated a DOT official to help work on the study. It would be the first such involvement at the actual working level of a federal representative.

The other major point of Adams' letter concerned itself with developing a long-range financing plan for both construction and operating costs.

He called for a meeting of local officials and DOT experts to deal with that problem. Metro is today operating on a one-year-at-a-time, hand-to-mouth existence. Local governments don't know how much subsidy to budget; Metro doesn't always know how much transit service it can provide.

These problems have received top priority from Metro's new general manager, Theodore Lutz, who also has been calling for longer-term, longer range financial planning. Local political officials first started that chorus when Lutz was an assistant secretary in the Ford administration's Department of Transportation.

Adams suggested in his letter that one possible source of money for both revenue bonds and other expenses might be funds transferred from abandoned interstate highway projects. Such money has been eyed by Metro supporters as a source of new subway construction. Obviously, the same dollars could not be used twice.

Local government officials had not received the letter last night and declined comment on Adams' proposals.