Transportation Secretary Brock Adams took a ride on the new Metro line to National Airport yesterday and said he is confident something will be worked out to keep Metro from defaulting on a $12 million debt it owes July 1.

Despite the fact the subway was delayed about 20 minutes on its return trip because it had blown a fuse, Adams said he was "very impressed."

But he did not offer any balm to Montgomery County, whose officials have reacted angrily to a letter from Silver Spring to Glenmont should not be built until all possible transportation alternatives are studied.

"The problem (with the Glenmont line) is that conditions have changed," Adams told reporters. "There have been enormous increases in costs. I am not saying that (the Glenmont line) will never be built."

Adams reaffirmed several times his commitment to the 60-mile Metro rail system that is presently under construction or under contract. But the region planned a 100-mile system, and several of those lines are currently under study at the direction of the Department of Transportation.

"I don't think (the 100-mile system) is unrealistic," Adams said, "but we will have to look at the alternatives." In "requesting" in his letter that the unfunded Glenmont line also be studied, Adams reversed a decision by the Ford administration that permitted the line to remain in the planned system without further study.

Montgomery County Metro board member Cleatus E. Barnett had charged at the Metro board meeting yesterday that "we have reason to believe that judgment (against the Glenmont line) has already been made at the (federal) staff level." Barnett emphasized he has no evidence.

Adams and his aides insisted during their tour that the Glenmont line had not been prejudged.

The line, 4.5 miles through deep rock, is the most expensive suburban link per mile in the system, and is estimated to cost $270 million to $275 million.

Montgomery County Executive James P. Gleason, in a letter to Adams, said that if the Glenmont line had to be restudied, "I will be forced to completely reconsider the extent of my support for future construction and financial commitments for the Metro system."

Members of the Metro board, including Virginia and District of Columbia representatives, supported Gleason's position yesterday and empowered board chairman Francis White to write Adams and, among other things, support the Glenmont line.

While the long-range political implications of the Glenmont line are great indeed, the most immediate concern at Metro, is how to meet a $12 million interest payment on Metro construction bonds that is due July 1.

The bonds are federally guaranteed. Metro general manager Theodore Lutz said during the board meeting that he was discussing two possible ways of paying the debt with congressional and administration officials . One would be a direct appropriation to the Metro authority, the other a one-time transfer of interstate highway money.

The highway money, has been previously transferred to Metro for subway construction. However, Lutz said recent bidding has brought Metro contracts in under estimate and some of the construction money might be available for an interest payment.

Lutz told the board he would "prefer to let the (federal) guarantee provisions work," and thus permit the bonds to go into default, than to tamper with money that is propping up the interim financial agreement to build 60 miles of subway.

Adams, standing on the National Airport platform, said yesterday that "I do not want those bonds to go into default." He said he was negotiating a solution to the funding crisis, and was confident some agreement could be reached.

Lutz conducted Adams on his tour, which began at the Department of Transportation building at 7th and D Streets SW. The new Metro line, to open July 1, has a station conveniently located in the DOT courtyard.