WASHINGTON, Oct. 28--A high administration official today defended the right of students and others to protest the war in Vietnam.

"Hanoi's misreading of American student protest demonstrations is not a sufficient reason for smothering debate in this country over the war in general," he declared. He spoke to some 650 editors and broadcasters at the State Department's bi-annual "background conference," which prohibits attribution of any statements.

The statement came in sharp contrast to recent harsh criticism by many high public officials of student demonstrations.

'Students today like to think they have a monopoly on demonstrating," the official quipped, " in my youth, I used to demonstrate myself."

He accused the demonstrators, however, of being "out of date." He said that those students who insist that the brunt of aggression is not from the North are no longer being realistic. "Even Hanoi no longer denies the assistance," he declared.

Officials at the conference brushed away the possibility that the United States might declare war against North Vietnam. They the Russians into a loss flexible position and might even provoke an alliance between the Russians and the Chinese.

The length of the war is unlimited, and the United States will continue its commitment until the opposition decides to negotiate, officials said. They reiterated the administration's position that it will enter into negotiations with out setting any preconditions.