Three months ago cost-conscious Montgomery County voters over-whelmingly enacted a charter amendment giving themselves new powers to vote on "certain" major county construction projects. The amendment left it up to the County Council elected at the same time, however, to decide what those "certain" facilities would be.

Yesterday, the council defined them, and when their lawyers had finished laying out the projects that were legally exempt, there was virtually nothing left.

Exempted from the referendum requirements were schools, many parks, colleges, public housing projects, water facilities, sewer projects, major highways and the subway.

"We have broken faith with the voters," said council member Rose Crenca, a leader of last fall's taxpayer's revolt who abstained yesterday.

Although debate on the measure during the election campaign stressed that the amendment would enable voters to defeat construction of some schools, roads and new government buildings they thought were too expensive, lawyers say now that this concept was never legal.

The county attorney's office told the newly elected council that it could not interfere with any project required under state law or by interstate or regional compact. That omits the public schools, Montgomery College, the Maryland National Capital Park and Planning Commission, State Highway Department, the Washington Suburban Sanitary Commission and several construction authorities, such as the Housing Opportunities Commission, which builds public housing projects with government-backed bonds.

The county attorney's office. which reviewed the amendment last summer, raised no questions about its applicability even though sponsor John Menke publicly stated many times that his intention was to let voters "get at" all costly public facilities, such as the new $50 million government center under construction in Rockville.

Council lawyer Philip Tierney said yesterday that he always thought "it was the intent of the previous council [which voted to put the amendment on the ballot] to have the [state and regional agencies] excluded."

According to council minutes, that point was never discussed.

The council decided yesterday that the only projects that will be covered by the amendment are construction projects that cost more than $4 million in county money excluding the cost of the land, the planning or the interest on the bonds.

The council staff has estimated that the only current projects that could have qualified would have been the new county office building, the new $150 million medical center near Gaithersburg, a sludge composting site and a regional park. Libraries and fire stations are not expensive enough to qualify.

The council, saying that yesterday's decision satisfied no one, passed the measure 6 to 0.

Council President Neal Potter said he questioned whether state law actually forbids the county from setting cost controls on some state and regional projects. Potter, however, said he was willing to let the dispute be settled by a court.