President Reagan ran a 101-degree fever last night after a partial collapse and inflammation at the base of his injured left lung earlier in the day. At one point his temperature rose to 102 before dropping to 99 yesterday afternoon.

White House physician Daniel Ruge said in a medical bulletin last night that a bronchoscope was used to remove "several small bronchial plugs as well as dormant blood" from the left lung. Dr. Ruge said Reagan's condition is "satisfactory" and that he remains "alert and generally comfortable."

Meanwhile, presidential press secretary James S. Brady was removed from the critical list at George Washington University Hospital, but he remains in intensive care.

According to the White House, when Brady's physician asked him yesterday what his job was, he replied "press secretary at the White House."

Reagan's surgeon, Dr. Benjamin Aaron, said that the president's "recovery to date has been remarkable," although he characterized yesterday as "a little bit of a setback."

Ruge said the president was put back on a "broad-spectrum antibiotic" that he received after surgery Monday, "pending the results of specific cultures."

Aaron said that since the operation to remove the explosive "Devastator" bullet that pierced his left lung, Reagan has been coughing up "old blood" that collected in the lung as a result of the wound.

Aaron said Reagan's fever probably was due to collapse of a small lung segment because blood clots blocked his breathing tubes.

The president was photographed yesterday for the first time since he was shot, and he met with his secretaries of state and defense, who were about to embark on foreign trips.

Secretary of State Alexander M. Haig Jr. left for the Middle East last night carrying letters from Reagan to leaders of the eight nations he will visit on the first Regan administration venture into the diplomatic tangle of Mideast politics.

Defense Secretary Casper W. Weinberger left last night to visit NATO nations in a trip that includes a nuclear planning meeting. There, he also will have the opportunity to press his European counterparts for commitments to united action should there be internal suppression or a Soviet invasion in Poland.

After his visit with Reagan, Haig was asked by reporters at the hospital about his widely reported disagreement with Weinberger in the White House Situation Room while Reagan was undergoing surgery Monday.

"I think the whole team performed magnificently, and the American people were well served by the team," Haig replied.

The president was informed by senior aides of the 88-to-10 Senate vote Thursday in favor of his budget-cut proposals and said, "That's tremendous," deputy White House press secretary Larry Speakes said.

The FBI confirmed yesterday that the bullet that struck Reagan, apparently after ricocheting off his limousine, was a "Devastator" designed to explode on impact. The FBI said it did not detonate.

Thomas Kelleher, chief of the FBI's laboratory division, said the bullet could have left a compound known as lead azide in Reagan's body, but he stressed that there is no evidence of leakage from the bullet into his body.

Kelleher added that although lead azide is toxic, it would not threaten the president's life. "It's a lead compound," Kelleher told United Press International, "and depending on the quantity you have in your body, it might make you sick."

Reagan's surgeon was asked about the president's trip to Mexico and California, scheduled to begin April 23, and indicated that any travel depends on how quickly the president regains his strength.

"Blood loss . . . is one of the more severe forms of trauma," Aaron said. "He probably, for a period of two or three weeks, will be tired very easily . . . and will have to have periodic rest periods."

Reagan should be able to begin working part-time in the Oval Office in about 10 days, Aaron added.

The medical report on press secretary Brady continued to be cautiously optimistic.

Brady "has gotten brighter every day since his injury," said Dr. Arthur I. Kobrine, who performed the 6 1/2-hour brain operation on Brady. "He speaks to me now with three-, four- and five-word sentences. If asked how he feels, he'll say to me, as he did today, that he feels fine."

Kobrine said that Brady moves his right side, which is controlled by the relatively undamaged left half of his brain, "close to normally," but he moves his left side very little.

It is too early to speculate about the extent of Brady's recovery because of the continuing risk of complications such as brain and lung infection or blood clots in the legs, Kobrine said.

"Under the very best of circumstances, he could end up with essentially no mental impairment" and "would walk with a cane and have some weakness of the left arm," Kobrine said.

"The worst case is, he can still die," the surgeon added.

For a year, Brady's condition can be subject to change, and any mental loss that remains after a year will probably be permanent, Kobrine said.

Aaron and Dr. Dennis O'Leary, dean of clinical affairs at George Washington University, who has been the principal hospital spokesman since Monday, were questioned yesterday about Reagan's condition when he arrived at the hospital.

"I think he might have been near shock when he first came in the hospital," Aaron said. "None of us was willing to sit around and see how much trouble he would be in."

Aaron said that even after a chest tube drained blood that had collected in Reagan's chest before he reached the hospital, "the blood was continuing to move out . . . at a rather alarming rate."

He said Reagan lost 3 1/2 quarts, or about half of his blood, and was given transfusions of about eight quarts.

At the White House, Speakes said chief of staff James A. Baker III had ordered a written study of the White House operation during the shooting crisis as a historical record.