Transportation Secretary Brock Adams told Metro yesterday that it could complete the design of the $347 million subway line from Silver Spring to Glenmont, but also said the line will still have to compete for federal money with four others in the system when construction comes.

"There is clearly not enough money available . . . to fund all five lines," Adams told Metro Board Chairman Francis White in a letter. The other four lines go to Greenbelt, Branch Avenue south of the Beltway, Vienna and Springfield.

It was the most explicit statement to date that the Metro system almost certainly will be cut back from the planned 100 miles, although the hand-writing has been on the wall in large federal script for more than a year.

Adam's letter also fell far short of giving Montgomery County Executive James P. Gleason the unfettered federal guarantee that he seeks for the Glenmont line. As a result, Gleason said yesterday, he intends "to use every power I have to hold back funds" for construction of 60 miles that regional and federal officials have already agreed to an interim pact.

Gleason, with the cooperation of Maryland state Transportation Secretary Hermann K. Intemann, has succeeded since July in withholding $328 million in federal money from approved Metro projects in the 60-mile plan.

Most of the work the $328 million is supposed to pay for is scheduled in Montgomery County on the Shady Grove line. But some of it also is scheduled for Washington and Virginia locations, and politicians in those areas have watched with increasing irritation as Gleason's tactics have held up construction.

Yesterday, Intemann abandoned Gleason's ship. He announced that he was signing the contract that would release the federal money and said he hoped "other things will not impede progress."

Lawyers in federal, state and Metro offices were scurrying to the fine print, however, to see if Gleason could still block the money as he promised to try to do.

The $328 million is the federal share of a federal-state partnership. There is also state matching money - about $44 million from Maryland in this case. That money must pass from the state treasury through an obscure state agency known as the Washington Suburban Transit Commission (WSTC) before it reaches Metro and can be used to match the federal money.

Gleason controls three votes on the six-member WSTC, which is normally nothing more than a conduit for federal and state money. Lawyers were studying what would happen if the state matching money was blocked by the transit commission. None of them - federal, state or Metro - would venture an opinion yesterday.

Adams' letter yesterday was a restatement and clarification of what the evolving federal position is on Metro. During the press conference at which he released the letter, Adams several times expressed exasperation at the slowness of local area officials in responding to federal requirements.

Adams said he had expected the report of the regional task force studying the four lines other than Glenmont by the end of October. But the study schedule of that committee has slipped for a number of reasons and it will not be completed until next year.

Local officials have also been irritated at what they see as a growing number of federal requirements to answer questions that the officials feel have already been answered. Each additional study, each new question, each new federal construction requirement, they maintain, takes time, and therefore costs money, but does not actually result in more completed construction.

A few more questions were added yesterday.

Adams forcefully restated his position that there will be no more federal Metro funds until the region has agreed on a plan to pay the costs of both building the system and operating it.

Local officials have insisted that they cannot answer that question until they know how much they are going to build.

"It's a Catch 22," Gleason said yesterday. He also called the requirement that the Glenmont Line compete with the other four uncompleted lines "a threat to cohesion: it pits one jurisdiction against the other."

An approved Glenmont line would give Montgomery County all of the subway it ever asked for. No other jurisdiction in the Metro area can make that statement yet.

The financial plan, which Adams said he wants "immediately," must answer several questions: how to pay for any construction beyond 60 miles and what that construction should be; how the deficit incurred in operating both bus and subway systems will be paid; and how the region's jurisdictions propose to pay off the $1 billion in revenue bonds that were sold to build Metro.

When Metro was planned, those bonds were to be paid back from revenues collected from Metro riders. But after the bonds were sold, with a full guarantee from the federal government, it became obvious that Metro would never make money or even break even. Thus there is a $1 billion debt that is uncovered.

Congressional appropriations cover 80 per cent of the interest for the current fiscal year; Metro will have to find the 20 per cent locally.

"I know this is difficult for the jurisdictions," Adams said," . . . but as a federal official, there has to come a date where you say it must be done."

Adams also said that further funding was conditional upon receipt of "a completed analysis of the social and economic impacts of each selected segment considering in particular the quality and equity of service for minority communities and the socially or economically disadvantaged."

It has long puzzled officials looking at Metro's map as to why there has been virtually no construction on the planned inner-city Washington line connecting 7th and 14th Streets NW with Anacostia. Many people who live there must use public transit because they do not have cars.

Meanwhile, Metro contractors have penetrated deep into the suburbs in Montgomery, Prince George's and Arlington counties and in Alexandria.

Adams also said yesterday that he still supports the $4.7 billion ceiling on total Metro costs that was levied by his predecessor, William T. Coleman Jr.

Adams made it clear that, although the costs of the Glenmont line weigh heavily against it in the federal views the approval of money for finishing design would permit rapid construction after the revised Metro system is decided on.

He also conceded that if there is to be a rapid transit system in the Glemont corridor - along 16th Street and Georgia Avenue from Silver Spring through Wheaton - that system should be "heavy rail" or subway, instead of buses of trolleys. Metro previously recommended - and Adams agreed yesterday - that costs could be saved on the Glenmont line by building smaller stations than those originally planned.

Any cut in the 100-mile Metro system that was laid out and approved in 1969 will deprive one or more jurisdictions of some subway service. Yet all area jurisdictions have contributed money - and that money went to build inner-city and inner suburban segments first. All the money is how gone, but the system is not complete. Who will reimburse whom? With what?

By insisting that Glenmont compete with the other four lines for funding, Adams has probably pushed to the front of the table an issue that local oficials know is there but have long tried to avoid.