A suggestion by Secretary of State Alexander M. Haig Jr. that the four American women who were shot to death in El Salvador last December may have been attempting to "run a roadblock" was denounced yesterday by relatives of the dead women who accused Haig of participating in "a subtle smear campaign."

Haig first made the suggestion Wednesday in testimony before the House Foreign Affairs Committee. He said there was some evidence that the women may have tried or "been perceived to have tried" to run a roadblock, which was followed by "an exchange of fire" that killed them.

Yesterday, appearing before the Senate Foreign Relations Committee, Haig tried to explain away the implications of his earlier remarks, asserting that he had been misquoted in some press accounts and that he was only repeating the "most prominent theory" about the killings among investigators.

That explanation, however, did not satisfy some of the relatives and colleagues of the dead women, who met yesterday with State Department and FBI officials and later said the United States appears to be "condoning" a coverup of the killings by the government of El Salvador.

The four women -- three Reagan Catholic nuns and a Catholic layworker -- were shot to death on Dec. 2 while on their way to El Salvador's capital of San Salvador.

William Ford, whose sister, Maryknoll sister Ita Ford, was among the victims, called Haig's comments "nonsence." He also quoted FBI officials and James R. Cheek, deputy assistant secretary of state for inner-American affairs, as saying there is no evidence the dead women were attempting to run a roadblock.

"We will be anxious to see if Secretary Haig is man enough to retract the nonsense he has been banting about," Ford said.

Ford and other relatives and colleagues of the dead women who met with reporters yesterday suggested they believe that comments such as Haig's were an attempt "to find some justification for the acts of the [government] security forces." Ford said that in all of his meetings with U.S. officials there has never been any suggestion that the women were killed by anyone but Salvadoran security forces.

They said they remain dissatisfied with the conduct of the investigation into the killings and are increasingly concerned about a "smear campaign" attempting to discredit the women by linking them to leftist insurgents in El Salvador.

Appearing before the Senate committee, Haig scoffed at questions suggesting that his earlier comments made it appear the woman could have been actively engaged in attempting to run a government roadblock. "My heavens, no," he said.

Haig said the shootings may have resulted in part from "panic" among the killers who tried to cover up the evidence of their crime.