A federally mandated analysis of the price of extending the Metro Red Line from Silver Spring to Glenmont shows that the cheapest alternative studied will cost $90 million more than Metro's present estimate of $270 million.

That figure, disclosed by sources attending the American Public Transit Association convention here, is bad news for Washington area officials who were hoping they could find a cheaper solution for the Glenmont line and thus resolve the complicated local political crisis on future metro construction.

Because of that crisis, all new construction on Metro has been suspended. A contract for two Metro stations - Tenley Circle and Friendship Heights - was awarded, but work has not begun. Other contracts scheduled for award, including the King Street station in Alexandria, have been held back to the consternation of northern Virginians.

This trouble began in early summer, when U.S. Transportaion Secretary Brock Adams ordered an anlysis of the contruction plans for the Glenmont line to determine if money could be saved, he 4.5 mile line, planned as a deep tunnel between Silver Spring and Glenmont with stops in Forest Glen and Wheaton, would cost more per mile than any other suburban section of the Metro system.

At the time the analysis was ordered, Adams left local officials with the clear impression that the line would be built when this analysis was completed. In a subsequent letter, however, he said the construction was contingent on a "cost effective" solution.

That letter infuriated Montgomery County Executive James P. Gleason, causing him to withhold his support for the release of $328 million earmarked for the construction of already designed and programmed segments of the Metro system.

Gleason said he would not favor releasing this money unless the federal government guaranteed the construction of the Glenmont line.

Maryland Transportation Secretary Hermann Intemann, who appears to have final control of most of that money, agreed to support Gleason for 60 days - a period which expires this week. Intemann has not said if he would continue to back Gleason's position.

The 60-day period was designed to allow time for the completion of the analysis, which is scheduled for review Thursday by the Metro board.

At the time the analysis was ordered, federal officials were understood to believe that 30 per cent could be cut from the $270 million cost through a realignment of the subway route and through innovative constructive techniques.

Instead, according to the sources here, the cheapest alternative and the one recommended by the consultant for Metro, will cost $360 million, an increase of 33 per cent. That recommended alternative would be a tunnel in the same alignment, with a new, cheaper design on the underground stations.

The second cheapest alternative, according to the sources, would be to go with the original tunnel and station design at a cost of $380 million, a 41 per cent increase over the previously estimated cost.

Various other design proposals were found even more costly, the sources said.

Richard S. Page, chief of the federal Urban Mass Transportation Administration (UMTA) and Adams' chief lieutenant in the Glenmont situation, refused to confirm the sources' figures yesterday.