Every time his Republican supporters think Richard Headlee, a colorful insurance executive, is going to start gaining on his Democratic opponent, Headlee shoots himself in the foot.

All fall Republican women have sniped at Headlee because of his opposition to legalized abortion and the Equal Rights Amendment. Elly Peterson, a former state GOP chairwoman, has endorsed his Democratic opponent, Rep. James J. Blanchard, 40.

So what did Headlee do last week? He told a radio interviewer that ERA sponsors "are proponents of lesbian and homosexual marriage."

This was enough to make Republican Senate candidate Philip Ruppe, an ERA supporter, disavow his ticket mate.

Headlee tried to recover with a written clarification but made matters worse. He said he had not meant that all ERA supporters were proponents of lesbian and homosexual marriages, only those who supported certain resolutions adopted by the Women's Assembly, a feminist rights gathering.

Cochair of the assembly was Helen Milliken, wife of Republican Gov. William G. Milliken. The governor's relationship with Headlee was already cool.

Milliken is a moderate, Headlee a conservative who defeated a Milliken-supported candidate in the primary. Asked if Headlee's appointment as a college trustee was "among the worst" appointments he had made as governor, Milliken replied: "I think it was the worst appointment I ever made."

The race is a major test for organized labor, particularly the United Auto Workers, who endorsed Blanchard, a chief sponsor of the Chrysler bailout, before the primary. The union is determined to make him Michigan's first Democratic governor in 20 years.