President Reagan is on a "spectacular" post-operative course following intestinal surgery at the Bethesda Naval Hospital, his chief surgeon said yesterday. But senior White House officials said Reagan would be on a reduced schedule and a light workload for weeks.

"I am amazed at how good I feel," Reagan told aides who greeted him less than 12 hours after surgery to remove a tumor from his colon. The president's doctors continued to express great optimism about his prospects for a full recovery.

Later, Reagan, experiencing a slight fever normal after such surgery, was reading a novel, walked around his room briefly and "is chomping at the bit to do a little more than his doctors want him to do," said presidential spokesman Larry Speakes.

Reagan was described by Speakes as "pretty much of an optimist" about today's expected report on whether the tumor was malignant.

White House officials said they are braced for a slower pace in the weeks ahead.

"It will be a much lighter schedule," said a senior official. "We'll try to make as many decisions as we can without involving him where we can get agreement, and if there is a difference of opinion, and it can't be ironed out, we'll make it crisp, succinct, and take it to him for a decision." The official added, "We would try to spare him as much of the details as possible."

White House chief of staff Donald T. Regan described in an interview yesterday how he had informally "tested" the president to determine if he was ready to reclaim the presidential authority he transferred to Vice President Bush before the surgery Saturday.

Regan said he and White House counsel Fred F. Fielding walked into the recovery room with a two-sentence letter to congressional leaders notifying them that Reagan was ready to reclaim his powers. The president, in a precedent-setting procedure, had temporarily transferred his powers to Bush during the operation to remove a section of his colon.

"I tried to test him to see, was he alert, from my layman's point of view," Regan said. "I asked him to read the letter he was about to sign. And by listening to him and by some of his statements and jokes, I knew he was damn alert and knew exactly what was going on . . . . "

Regan said he offered to come back with the letter in an hour. "Hell no!" Reagan responded. "Then I wouldn't sign the letter. Gimme that."

The president's signature on the letter reclaiming his authority began a process by which the White House sought to reassure the nation that he had not been impaired. At the same time, officials also laid plans to ease the burden of his duties during a recovery expected to take six to eight weeks.

The portrayal of Reagan as actively engaged in presidential business began early yesterday. Speakes announced that Reagan "expressed a strong desire to see action on the federal budget this week." Reagan said, "I want to emphasize this week," Speakes reported.

Reagan is to remain at Bethesda Naval Hospital until early next week.

Chief of staff Regan said the federal budget was the last thing he spoke to the president about before the three-hour surgery Saturday, and the first thing Reagan asked about after the surgery. The president also asked about the seven Americans still held in Beirut, he said.

Regan said the president was "puzzled" and "disappointed" by criticism from Senate Majority Leader Robert J. Dole (R-Kan.) that the president had "surrendered" in the battle against the deficit.

"He's not throwing in the towel," Regan said.

Presidential aides were also talking optimistically about the president greeting Chinese President Li Xiannian at the White House July 23. "There will be events that will be natural to show the president on his feet," said the White House official.

Speakes said the president asked for newspapers -- "only for the comics," he joked -- and received a national security briefing yesterday as well. The White House also highlighted positive reports on the president's recovery.

Speakes said Reagan was "virtually pain free." A senior White House official said the president was experiencing some tenderness in his throat, presumably from a nasal-gastric tube.

Speakes quoted Dr. Dale Oller, the hospital's chief of surgery, as saying Reagan's vital signs are "rock stable," including his temperature, pulse, and blood pressure. Speakes also quoted one doctor as saying Reagan had "the internal workings of a 40-year-old."

The White House made public an official photograph of the president kissing his wife, Nancy, yesterday morning. It was the first time Reagan had been photographed since entering the hospital Friday.

Although the White House was quick to immerse Reagan again in budget and foreign policy discussions, senior officials said the recuperation and reduced workload would extend for several weeks, probably through Reagan's scheduled August vacation in California.

A senior official said a planned trip to Wyoming July 24-25 would probably be scrapped because Reagan would not be ready to return to speech-making.

The official said the surgery would also "disrupt" some planned ceremonies and meetings at the White House in which Reagan was scheduled to participate.

The question of Reagan's recovery schedule is important in light of the after-effects of surgery in 1981 following the attempt on his life. The recovery then had the effect of postponing many key personnel decisions and other matters.

The White House official said an effort would be made to "spare" Reagan from listening to policy debates. "Boil it down, put it on paper," the official said.

Regan is keeping control over the president's schedule, officials said. Cabinet members, Vice President Bush and the White House staff will act as surrogates for the president while he is recovering, the White House official said.

But he added that there is "no seeking of power or somebody trying to say who's in charge here. It's not that," a reference to then-Secretary of State Alexander M. Haig Jr.'s controversial claim after Reagan was shot in 1981.

It was also disclosed yesterday that Bush had been in frequent contact with Regan late Friday and early Saturday morning about the transfer of power. Such a transfer has never before been attempted using the procedures of the 25th Amendment to the Constitution.

Bush abruptly left his vacation home in Kennebunkport, Maine, early Saturday morning. His aides said then Bush was returning out of "personal" concern for Reagan.

But a senior White House official said Bush and Regan had talked about the transfer of power into the early morning hours Saturday and Bush was fully aware of it. Bush had a duplicate set of equipment with him to handle any "national emergency," the official said. The official was not more specific but this was apparently a reference to secret equipment to control the national defense in the event of a nuclear attack.

"We had this procedure all set up," the official added. Bush was told by Regan, "Be prepared" to assume power, he said.

Bush expressed concern that he would be in the air flying back to Washington when the transfer of power took place, the official said. But Regan reassured him, "you'll be in charge."

As it turned out, Bush was apparently informed that he had become acting president upon arriving at Andrews Air Force Base, about 12 minutes after Reagan had gone under anesthesia.

Bush's plane, Air Force Two, carries sophisticated communications equipment that Speakes said was capable of putting him in contact with aides at the hospital.