Senate Majority Leader Robert C. Byrd said yesterday that President Carter "did what he had to do" in firing Maj. Gen. John K. Singlaub as U.S. chief of staff in South Korea.

As a result, Carter will not be subjected to the congressional criticism and national reaction that surrounded President Harry Truman's dismissal of Gen. Douglas MacArthur in 1951, said Byrd (D.W.Va.).

Both Singlaub and MacArthur got into trouble for publicly opposing their bosses' Korean policy. Singlaub was dismissed Saturday as chief of staff for telling The Washington Post earlier last week that Carter's plan to withdraw U.S. ground troops from Korea is a mistake that would lead to war.

Truman dismissed MacArthur on April 11, 1951, because of the general's presistent public demands for a wider war against Communist China - contrary to U.S policy and that of other United Nations countries supporting the war in Korea at that time.

Within two days after Truman's action, the White House was inundated with 125,000 telegrams supporting the popular MacArthur. There also were congressional calls to impeach Truman.

Byrd, appearing on "Meet the Press" (NBC, WRC), bluntly replied, "No," when asked if he thought Carter would become embroiled in a controversy similar to Truman's.

"He did what he had to do," Byrd said. "He didn't really fire him. He relieved him of his responsibilites as chief of staf in Korea. He'll be reasisgned somewhere else. I think he had no choice but to do this."

Defense Secretary Harold Brown said yesterday on "Face the Nation" (CBS, WTOP) that Singlaub's reasisgnment is necessary because "his effectiveness is undermined" in South Korea because of his outspoken opposition to Carter's policy.

Brown said he believes another "useful place" can be found for Singlaub, whom he described as a "capable and dedicated officer."

Brown said Singlaub's reprimand was not meant to curb freedom of speech in the military.

The military are not only allowed, but they're encouraged to express their views during the determination of policy - through the chain of command," Brown said.

"However, once a military person has had a chance to express his views on a policy that's being determined - and the policy is determined - it therefore becomes his responsibility to support that policy publicly, if he plans to stay in the military," the secretary said.

Asked if Singlaub's dismissal is a "black mark" on the general's record, Brown said: "Getting this much publicity of this kind I'm sure is not something that he likes. It's part of his history now."