On Good Friday, as vacation-bound President Reagan headed to Santa Barbara on Air Force One, deputy chief of staff Michael K. Deaver examined the draft of the radio speech Reagan was supposed to give the next day. Deaver didn't like what he saw.

White House officials said the speech, which had been approved by communications director Patrick J. Buchanan, was heavy with Easter and Passover themes and struck Deaver as "a sermon" and "very preachy kind of thing."

What most concerned Deaver, according to one knowledgeable official, was that the speech would be perceived as hypocritical because Reagan would be relaxing at his ranch on Easter Sunday rather than going to church. Deaver killed the speech and substituted one that dealt with two items high on Reagan's agenda, the budget and Nicaraguan policy.

The action was a typical and timely demonstration of the influence wielded for the past four years by Deaver, maestro of many of Reagan's most successful media events, and the aide having the closest personal relationship with the president and his wife, Nancy. But Deaver will strike out on his own May 15, when he leaves the White House to open a public relations firm.

Other Reagan intimates and White House officials disagree on whether anyone can fill Deaver's shoes. Some say Reagan will sorely miss the "Deaver touch" in scheduling and staging; others observe that Reagan showed mastery in dealing with the news media long before Deaver was his principal guide.

But there is widespread agreement that no one will be able to attend to Nancy Reagan's needs as Deaver did. And some present and former officials say Deaver has been a force for moderation that will be missed in the White House on such key issues as arms control and civil rights.

"Mike is a non-confrontationist, a non-ideologue," said Kenneth M. Duberstein, Reagan's former chief of legislative affairs. "He worries about Reagan and Nancy. You get all the competing forces, and Mike asks, 'What's best for Ronald Reagan?' "

Deaver's departure will close a long chapter in Reagan's career marked by dependency on a cadre of loyalists who served him since his two-term California governorship. Gone is William P. Clark, his longtime troubleshooter in many sensitive roles. Gone from the White House is Reagan's former counselor, Edwin Meese III, now attorney general.

But for all their importance, neither Clark nor Meese has been as close to the president as has Deaver, whom Reagan treats as a son and trusts as an adviser.

"Mike's value is that he had a close and intimate relationship with Reagan before Reagan became president," said Craig L. Fuller, chief of staff for Vice President Bush, who worked for four years with Deaver in his public relations firm and another four years in the White House. "Deaver knew in advance how the president would react. He was the ideal person, maybe the only person, to determine how Reagan spent his time both on public relations and on issues."

Deaver's reputation was formed on an intuitive sense of Reagan's needs and an acquired understanding of media requirements in a television age. He has emphasized "visuals" and "backdrops," recognizing that Reagan's strength is often the overall impression he conveys rather than what he says.

"First of all, it's pretty hard to make Reagan look bad, so we start from that premise," Deaver said in an interview with The Washington Post. "And secondly, I do think the visual is extremely important in a television age."

Early in Reagan's first term as president, Deaver watched him give an address from the Oval Office and was bothered by the way it looked on television.

"I finally figured out it was the tan curtain they put behind his desk," Deaver said. "His head got lost in that color . . . . So I went in there with the lighting people and I said, 'I want the curtain open.' They said I couldn't open the curtain because the lights from the camera will bounce off the windows. I said that is not a good enough answer and got a lighting expert from New York City and he came down here and lit the windows from the other side . . . . Now you have a wonderful visual of the president of the United States with trees and green or snow, and it opens the whole thing up and gives a much warmer feeling than the tan curtain that just stopped everything."

Deaver selected aides with a similar eye for detail, notably scheduler Frederick J. Ryan Jr. and director of advance William Henkel. They favored blue backdrops and dramatic settings that illustrated the story Reagan was trying to tell.

Explaining why he selected the New York Stock Exchange for a recent Reagan speech on the economy, Deaver told the New York Daily News, "The evening news bit reaches 80 million people. That's why we spend so much time on the visuals -- so that a person watching for 50 seconds not only hears the president's words but sees him in this financial setting. Even if the networks end up using him answering a shouted question on the MX, they've still got to explain what he was doing at the stock exchange."

Throughout Reagan's reelection campaign last year, Deaver's control of the schedule and his close working relationship with strategist Stuart K. Spencer enabled him to use presidential trips for political dramatization. When the administration wanted to make a point about the upturn in housing starts and couldn't sell the story in Washington, Deaver sent the president to Houston, where housing was booming, to make his case on television.

"What Deaver brought was an insight into what Ronald Reagan does best -- what he would be most effective at," said White House spokesman Larry Speakes. "Should he do a one-on-one or take his show on the road? He has an instinct for knowing Reagan. He knew how Reagan would play."

Deaver also has an understanding of Reagan's shortcomings and of the president's penchant for answering questions off the top of his head whether or not he knows the answers. Out of this understanding, early in the administration, came "the Deaver Rule": The president would not answer questions during the numerous White House picture-taking sessions.

The rule helped the president's aides focus network attention on the event they wanted to be the story of the day rather than on news created by the president's response to questions on other topics. But Reagan, whose preference is to answer questions, frequently broke the rule, sometimes with unfavorable results. Once, the president absent-mindedly said by mistake, "I don't take questions at news conferences."

Deaver has had his share of lapses, too, as he has acknowledged in interviews and private conversations. At present he is being criticized by other administration officials for not foreseeing the political hazards of agreeing to a West German request to have Reagan lay a wreath at a cemetery containing Nazi war dead during the president's European trip next month.

In Deaver's view, his most serious error occurred on Reagan's 1982 European trip, when the president was so overscheduled and tired that he nodded off during a televised meeting with the pope.

It was a mistake that was rarely repeated. When Reagan subsequently visited the People's Republic of China, Deaver prepared him for it with a leisurely advance week that included several days at his ranch and stopovers in Hawaii and Guam. Reagan's performance was vigorous.

Some longtime Reagan intimates credit Deaver with "broadening" the president's horizons by scheduling that exposed him to diverse views in private meetings with peace activists and social critics of the administration.

"Mike will always wind up doing the right thing," Reagan strategist Spencer once observed.

In the critical year 1984, when Reagan dropped the phrase "evil empire" from his vocabulary as a synonym for the Soviet Union, it was an open secret in the White House that Deaver and Nancy Reagan had joined forces in favor of a more accommodating position toward the Soviets on arms control.

Deaver's advocacy was not lost on conservative critics of Reagan. In a Dec. 2, 1983, column in The Washington Times, Buchanan took aim at then-White House chief of staff James A. Baker III and Deaver, who he said was "the treacherous 'Lord Chamberpot' in the demonology of the New Right."

After Donald T. Regan became chief of staff and hired Buchanan as communications director, Deaver is known to have told the conservative former columnist that he deemed the appointment inimical to Reagan's interests. Buchanan reportedly replied that he would be a team player.

"The real question isn't whether Pat will be a member of the team," said an official who sometimes has criticized Deaver but laments his departure. "The real question is who will look to Reagan's own interests, apart from the agenda of the conservative movement. Reagan is a conservative, but his interests are not always identical with the movement's."

On the surface, Deaver, 47, seems as unlikely a choice for a president's principal aide as Reagan once seemed an unlikely candidate for president. The son of a Republican gas station owner in the California oil town of Bakersfield, Deaver's only observable talent as a young man was a gift for piano playing. It made him popular at his college fraternity at San Jose State and helped him raise enough money to get home when he was traveling around the world with a friend and became stranded in Australia.

But Deaver was obsessed with organization, particularly political organization, and, some of his longtime friends say, with a desire for influence and recognition.

"As long as I can remember, I always wanted to be a part of an organization or institution that influenced change," Deaver recalls. "I wanted to be part of the action . . . . And when I leave here I don't want to just go to work for a corporation. I don't want to just have a list of clients. I want to be able to, with those clients, solve their problems and change once again the world into a better place."

Not all of Deaver's colleagues would agree with his description of himself. Within the White House he has been criticized privately as overly fond of perquisites and not substantively involved in issues.

Deaver acknowledges that he did not gain detailed mastery of many issues but says that this reflects his understanding of his strengths and weaknesses and a conscious decision on setting priorities.

"I think my strengths are not being afraid to make a decision, right or wrong, my understanding of the communications medium and my ability to get people together and act as an expediter on a problem," Deaver said.

Even many of Deaver's critics would agree with his assessment. One staff member, recently attending his first meeting chaired by Deaver, said "it was as terse and businesslike and well-organized as any meeting I have ever seen."

Over the years Deaver has formed alliances and broken them. Those who lost out say that his behavior was sometimes unfair or capricious. He played an important role in the selection of Baker as chief of staff and often teamed with him during the first term against positions advocated by Clark and Meese. The partnership benefited both men, with Baker providing the outside political savvy and Deaver the understanding of Reagan.

In the process, Deaver and Clark became enemies. Ultimately, according to many accounts, it was Nancy Reagan's support for Deaver that caused Clark to leave the White House.

Earlier, in the 1980 campaign, Reagan exploded into rare fury when a dispute on strategy between Deaver and the then-campaign manager, John P. Sears, provoked a Deaver walkout. Reagan let Deaver go temporarily but eventually took him back and fired Sears.

"When the crunch comes, Reagan has always sided with Nancy and with Deaver," a presidential intimate said. Now, as Deaver prepares to leave the White House, a large question remains as to how Reagan will fill the void. Some expect Deaver to be consulted on media strategy, but others believe that Buchanan will move quickly to acquire authority over strategy and scheduling.

Whatever happens, it is unlikely that any one person will fill the role that Deaver has come to play in his 18-year association with the Reagans.

"Reagan is extraordinarily personable but forms few close friendships," one senior official said. "Mike is at the top of the list, both with him and Nancy. With the close relationship there is respect for his judgment, which is rare in Washington and especially in the Reagan White House. I think the president is going to miss having Mike at his right hand."