Secretary of State Alexander M. Haig Jr. yesterday refused to comment on reports that alleged Libyan assassination squads have suspended their attempts to infiltrate the United States, but he added that "if such reports are true, it underlies the validity of the steps taken by the president."

Haig's statement, made during an interview with The Washington Post, appeared to refer to the heavy additional security instituted for President Reagan and other U.S. officials in the month since U.S. intelligence agencies reportedly learned that the hit squads were dispatched by Libyan leader Muammar Qaddafi.

The administration has refused to make public its evidence about the existence of the hit teams, and last week there were reports that U.S. intelligence agencies now believe the teams have suspended their operations.

Haig also said he is "optimistic" that the strain in U.S.-Israeli relations caused by Israel's annexation of the Golan Heights and the subsequent U.S. suspension of a strategic cooperation agreement has been eased.

Asked whether the United States might feel compelled to support U.N. sanctions if Israel refuses to rescind the Golan action, Haig ducked a direct answer. But he added: "I would certainly hope not . . . . I would not expect a further aggravation in our relations. I'm optimistic."