President Reagan's intermittent fever has forced a delay in his release from the hospital, but a chest X-ray yesterday showed "modest clearing" of the traces of dried blood and dead tissue along the path of the bullet that pierced his left lung.

White House aides said Reagan probably will return to the White House late this week, but doctors treating the president at George Washington University Hospital refused to commit themselves. Dr. Dennis O'Leary, spokesman for the hospital, had predicted before the president's first fever on Friday that Reagan would be able to return to the White House early this week.

Reagan was running a slight fever, around 99 degrees, yesterday.

"He looked fine and said he felt good," White House chief of staff James A. Baker III said after visiting Reagan for about 15 minutes yesterday morning with White House counselor Edwin Meese III and deputy chief of staff Michael K. Deaver.

Soon after the president's release from the hospital he is likely to make a nationally televised appeal for his tax-cut proposals, Baker said.

Reagan would like to make his speech before income tax day, April 15, Baker said, "but that might not be possible."

The personal income tax reduction of 10 percent annually for three years has far less popular support than do his proposed cuts in federal spending, according to polls, and White House planners had intended before the assassination attempt to devote much of last week and this one to attempts to build support for the tax side of the president's economic program.

A medical report issue by the White House press office yesterday said there is no evidence of bacterial infection, but as a precaution Reagan has been given a wilder range of antibiotics to protect against a greater variety of bacteria.

"The president continues to be alert and in good spirits," the statement said.

Baker said Reagan is being given paperwork each day that takes him between an hour and 75 minutes to read. "We are not sending over items that can appropriately be deferred," he said.

In addition to his senior staff aides, Reagan was visited yesterday by his wife, his daughter Maureen and House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.).

The president had planned to travel tomorrow to Cincinnati to throw out the first ball on opening day of the baseball season. White house deputy press secretary Larry Speakes announced yesterday that Vice President Bush will not substitute for Reagan at the game because the president will not be back in the White House by then and it is considered better for Bush not to leave Washington.

Yesterday at a White House ceremony proclaiming May 1 as Law Day, Bush condemned that attempted assassination.

"Violent crime is the uncivilized shout that threatens to drown out and ultimately silence the language of liberty," Bush said. Speakes also announced that Australian Prime Minister Malcolm Fraser has accepted Reagan's invitation to make an official visit to Washington June 29 to July 1.

Press secretary James S. Brady, the most seriously wounded of the four men shot March 30, "continues his thus-far uncomplicated recovery," the medical report issued by the White House said.

His thinking processes and speech continue to improve and he "now makes quips and jokes spontaneously," it added. Brady, who underwent a 6 1/2-hour brain operation, got his first look at his surgeon, Dr. Arthur Kobrine, and remarked, "Not a bad job, doc," the statement said. Brady's vital signs were reported normal.

Secret Service agent Timothy McCarthy and D.C. policeman Thomas K. Delahanty also continue to recover, the report said.