President Reagan said in an interview broadcast yesterday that the 1973 War Powers Resolution is "illegal" and "unconstitutional" and that he does not intend to invoke the notification procedures despite recent military conflict with Iran in the Persian Gulf.

In some of his strongest remarks yet rejecting a voice for Congress in the U.S. tanker escort operation, Reagan said in the interview with CNN, "There are some things that have to be vested in the commander in chief. One example, and I think we did it right, was Grenada.

"The idea of a legislative body having to get together and fight over and vote on something at the same time that our national security is endangered, I just don't think it could be done," he said.

The War Powers Resolution requires the president to notify Congress when U.S. forces are involved in "imminent hostilities," and such a notification starts a process by which the forces would be withdrawn after 90 days unless Congress votes to continue their deployment.

Congress has been divided all year over applying the law to the Persian Gulf situation, and Senate leaders this week proposed a sharply scaled-back compromise version.

Yesterday Reagan stopped short of the formal War Powers notification procedure that many on Capitol Hill have demanded when he sent letters to congressional leaders saying the United States took "limited defensive action" in connection with last week's gulf incident and "we regard this incident as closed."

White House spokesman Marlin Fitzwater said Friday that the administration was not invoking the notification procedure in current law because recent confrontations in the gulf were "isolated" incidents that did not portend imminent hostilities. Fitzwater denied that the White House was ignoring the law and asserted that administration officials had made a case-by-case determination that the notification procedure did not apply.

Reagan took a much broader view in the interview, suggesting there are no circumstances in which he intends to invoke the current law. "We think that what the War Powers Act -- first of all, we think it's illegal. We think that one part of it. . . is unconstitutional," he said, referring to the clause giving Congress a vote over the deployment of U.S. forces.

"And if you look at our history, we have had only five declared wars in the history of the United States," he said. "Presidents have sent into military action military forces of our country some 200 times."

Reagan said a president should consult with Congress when "actually deploying troops in a hostile manner against forces in another country," but should not have to ask "permission" for such efforts as the tanker reflagging operation because it would shake the confidence of other nations.

On the subject of arms control, Reagan said he believes the Soviets have relaxed their earlier demands that any agreement on limiting strategic nuclear weapons be linked to restrictions on his Strategic Defense Initiative (SDI), the proposed missile defense system. "I don't think they have actually linked it to a weapon proposal now and, as they did at Reykjavik, made it plain that there could be no agreement unless it included SDI," he said.

Reagan also asserted, as the administration has before, that the 1972 Antiballistic Missile Treaty allows the research and testing of SDI. Reagan did not mention it, but administration policy has been to honor a more restrictive interpretation of the treaty while maintaining that the broad interpretation is legally correct.

Despite criticism from the allies and others who believe that some nuclear weapons should be retained, Reagan said it is still his view that if strategic weapons could be cut in half, "I would like to think that we would be on our way to the total elimination of nuclear weapons."