Harvard experts yesterday criticized President Reagan's Thursday night speech in which he justified arms transfers to Iran, calling him unconvincing and charging that he attempted to conceal his motives for making the deal.

However, the scholars said they thought the address would not affect Reagan's popularity.

In his nationally broadcast speech, prompted by widespread criticism among Congressional and other government officials, Reagan revealed that he had secretly authorized the transfer of defensive weapons and spare parts to Iran in part to "replace the animosity" between the two countries.

Critics said yesterday that in his speech Reagan downplayed what they believe to be his true motive in the deal: to secure the release of three U.S. hostages previously held in Lebanon.

"It was a very lame explanation," said Baird Professor of History Richard Pipes, a former National Security Adviser to Reagan, referring to Reagan's desire to reopen communication between Iran and the United States. Pipes, an expert on the Soviet Union, said Reagan should not have attempted to conceal U.S. dealings with Iran, and described the President's current situation as "a mess."

Laurie A. Mylroie, an assistant professor of government specializing in the Middle East, said Reagan did not clearly address the issues involved. "He said he was going to give the facts, and he didn't," Mylroie said.

Some scholars charged that Reagan remarks were simply insincere, and were intended to mask his actions.

"It doesn't seem as though there was any indication of improving relations with Iran aside from releasing hostages," said Dunwalke Associate Professor of History Alan Brinkley.

"His reference to the strategic importance of Iran was a cover-up," said Sepehr Zabih, a research fellow at the Center for Middle Eastern Studies.

While most professors expressed dissatisfaction with the President's remarks, few said they thought it would damage his image.

"He has an excellent track record," said Kennedy School Professor of Public Policy Albert Carnesale, referring to Reagan's previous success in deflecting public criticism of his administration's policies.

"People feel [Reagan] is telling them what he believes--that is why his popularity is so great," said the expert on the nuclear arms race.

Assistant Professor of Government Henry E. Brady said Reagan's speech had the immediate effect of calming public opinion. "But, there are still many unanswered questions," he said.