Every morning at 7:30, in a spacious, yellow-walled room down the hall from the Oval Office, three men meet over grapefruit and cereal to draw up the daily marching orders for the 351 people on the White House staff.

Next to President Reagan, the three men are the most powerful in Washington. They speak for the president and act in his name: counselor Edwin Meese III, chief of staff James A. Baker III and deputy chief of staff Michael K. Deaver.

The president is still asleep when Meese, Baker and Deaver hold their first meeting of the day in Baker's office. By the time of their last meeting of the day, Reagan will be back in the residence resting again.

No one questions the authority of the three men, who refer to themselves as "the Triumvirate" and are called by others, "the Big Three." It is a familiar, if not entirely accurate, joke at the White House that the three of them are never seen anywhere alone. But they are a team.

Under a picture of the president and the Big Three in Meese's office an irreverent member of the administration once pasted the words, "Ronald Reagan and the Three Stooges." Reagan is also used to seeing them together. When the three saw him in the hospital after the March 30 assassination attempt, the president's first words were, "Who's minding the store?"

Four months into the Reagan administration the Triumvirate is already an unlikely legend. In a town that takes the White House chiefs of staff seriously, a tripartite sharing of power seems as impractical as a three-cylinder engine. Yet, thus far, it seems to work.

Maybe, the skeptics said, the new president with his laid-back California style needed someone like Deaver to keep his schedule and look out for Nancy Reagan. But the division of power between Baker and Meese seemed certain to produce a power struggle, the kind which had ensued between President Carter's Hamilton Jordan and Jack Watson. History argued that either Baker or Meese must inevitably wind up in the cold.

It hasn't happened that way. Why? Most of all, because Reagan does not want a power struggle around him and, says Deaver, because each member of the Big Three is personally secure. Most of the time, they have as few differences over turf or issues as they do in deciding on their breakfast.

The key to the sharing of power between Meese and Baker is that they can speak for each other as well as for the president. While Meese is ostensibly in charge of policy and Baker in charge of operations, they are interchangeable in dealing with other staff members or the outside world.

"I am constantly amazed at their lack of personal aggrandizement," says U.S. trade representative Bill Brock, who has experience with six presidents and their staffs" . . . There are times when I call one to get a decision that is primarily in his area, and I can't reach him because he may be out of town or in a meeting or something and I'll call the other. . . . I know that once I've gotten that answer that the first person I called will agree with it. Never have I seen one of them come back on the other and try to roll the decision."

This is admittedly a springtime portrait of a new administration flushed with early successes. But will this new spirit of collegiality in the Reagan White House withstand the first crisis that flares up without warning, the first public scandal or miscalculated statement that produces a political defeat?

Will the equanimity of the Triumvirate survive the inevitable hard tests which have yet to rock the Reagan administration?

Everyone can share credit for triumphs, like the Democratic House accepting a conservative Republican budget, but blunders are orphans, like the bad timing of the administration's controversial Social Security plan.

Even with the Triumvirate's successful beginning, the decision-making structure of the Reagan administration contains the potential for real failure.This series of articles, as it describes how that decision structure works to make high policy, will also examine some trouble spots that are already apparent to insiders.

The most serious one is one of the most important: the White House process for foreign policy decision. Other questions focus on the Reagan innovation of Cabinet councils which have yet in many cases to function fully as envisioned.

But for now, the Reagan White House is working, and mostly because of the Triumvirate. As long as they stay together, and speak for each other, it is almost impossible for them to be outflanked by even a bureaucratically skilled Cabinet member.

Their schedule of meetings does not capture the full importance of the Triumvirate, because much of the work is done by personal communication outside the meeting process. They start each day in Baker's office, a session both focused and relaxed, then proceed to a senior staff meeting in the Roosevelt Room with 20 or more high White House aides. Baker chairs the meeting, and Meese usually takes over if Baker is absent.

At 9 a.m. the trio meets with the president in the Oval Office, 15 minutes later than before Reagan was wounded. They usually bring him a completed agenda for the day upon which all of them already agree.

"There's a lot of laughing and kidding around at that first meeting in the morning," says a White House aide. "There's less of it when they get together at the end of the day, because everybody's tired then."

The joking is situational and some of it unprintable, although there are certain well-worn themes.

Meese takes a ribbing for his supposed disorganization, a subject on which he can be sensitive when it is raised outside the Triumvirate.

Deaver is kidded about being "a glorified bag-toter" whenever the inevitable press references to "Reagan's closest aide" appear.

Baker is "the Preppy," a jibe both at his own less-than-humble origins and his campaign association with that quintessential preppy, George Bush. The vice president takes a bit of ribbing on this score himself. When Deaver learned that Bush changed watch straps to match his suits, he began carring spare straps with him so he could offer one to the vice president when he passed him in the hall.

Meese, 48, a San Diego lawyer with a deceptively amiable manner, is typecast as Reagan's counselor. He shares his president's philosophical premises, understands how Reagan thinks and frames policy decisions in ways acceptable both to the president and to his constituents.

He also has the liabilities of his assets. The chief liability may be that Meese, because his counsel is so highly valued by Reagan, plunges into every policymaking area, and there are those at the White House who believe he is severely overextended.

Nonetheless, Meese is probably more influential as counselor than he would have been as chief of staff. He benefits from the presence of Baker, who at the White House is considered a better nuts-and-bolts man. Meese's passion is law enforcement, on which he is well-informed and takes propolice positions which have both reflected and shaped Reagan's views.

Meese guided the timing of the public announcement of Reagan's pardon of two former high-ranking FBI agents so he could announce it simultaneously to a law enforcement group he was addressing in California.

Baker is the politician of the Triumvirate, a skilled Texas lawyer who ran campaigns for Gerald R. Ford and George Bush when they were Reagan opponents. When he came over to the Reagan camp, there were those who kidded him, and it had something of an edge to it, that this was the only way Baker could find a winner.

In the Reagan campaign, some tried to consign Baker to a subordinate role and keep him away from the candidate. Meese, whose greatest strength is his collegiality, made sure that Baker was included in the high councils. Baker, who negotiated the ground rules for the debate which President Carter accepted and lost, did the rest.

At 50, Baker looks the youngest, but is the oldest of the three. His strength is his skill at making rapid-fire decisions and in following through on them. However, he has not known Reagan well or long, and his success has been aided -- some would put it far more strongly -- by the presence of Deaver, who is personally close to the president and adept at reading his moods.

"He's both strong and compassionate, and that's an unusual combination," says his executive assistant, Margaret Tutwiler. "He's Mr. Everything in Houston -- comes from one of the oldest families, successful lawyer, tons of money. That gives you a type of security that makes you a more powerful person because you don't need the job to be somebody back in your hometown."

Deaver is the non-lawyer of the group, the one who brings the human dimension to questions. He has been with Reagan even longer than Meese, and he knows the president's strengths and limitations.

Nancy Reagan likes and respects Deaver. He considers her a friend and the administration's underrated asset. At 42, the balding Deaver is the youngest member of the Trimvirate and the one most attentive to "little things" like autographs and pictures and the birthdays of staff members. In the White House, people remember the little things all their lives.

"Mike's the underrated one," says one of the many Californians who has come to Washington with Reagan. Deaver, who started as a night club piano player without any particular training for government, has matured steadily on the job since he first came to work as an assistant for Gov. Reagan's executive assistant, William P. Clark. And Deaver's self-effacing, low-key manner has often made him seem less important than he really is.

Friends say Deaver has grown to dislike the description which seems to fit him best -- "the perfect adjutant" -- which seems to imply that he is little more than a coat carrier.

When the conflict on foreign policy process between the White House and the State Department was particularly tense, the frequent telephone calls between Deaver and Clark, who is now Secretary or State Alexander M. Haig Jr.'s deputy, became a useful back channel of communication.

Given Deaver's closeness to Reagan and his skill at communications behind the scenes, Baker and Clark use another word than "adjutant" to describe this unassuming Californian who likes to tell off-color stories. The word is "catalyst."

When Reagan chose Baker as his chief of staff the day after the election, there were lots of raised eyebrows among the Californians. Baker had been "Bush's man," after all, and before that Ford's. In a move that would presage their relationship in the White House, Baker and Meese sat down together and divvied up authority.

As chief of staff, Baker became the White House chief administrator with responsibility for administration and politics, including personnel, communications, speechwriting, the press office, intergovernmental relations, public and legislation liaison, the White House counsel, scheduling and advance.

"Who controls the staff controls the White House," is vintage Washington aphorism, one that recalls the pervasive power of chief of staff H.R. (Bob) Halderman in the Nixon administration. But in the Reagan administration, this adage, along with a lot of other conventional wisdom, has been thrown overboard.

Baker controls the staff, all right, but this frees Meese to live up to his title of counselor.Meese has policy responsibility, which means that both the National Security Council, directed by Richard V. Allen, and the Office of Policy Development (the old Domestic Council), headed by Martin Anderson, report to him. This guarantees that Meese has a shaping role in the way policies are framed for decision by the president. But it is an authority Meese uses carefully, and with great skill.

"Putting George Bush in charge of crisis management was a Meese idea from beginning to end, even though Baker an others were involved," says a well-placed White House official. "It didn't seem controversial when it went to the president, because everyone was on board." As it turned out, "everyone" referred to the White House insider and not to a key player who dissented: Secretary of State Haig.

Baker has an impact on policy that transcends his operational role. It was Baker who prodded others in the White House to have the president lift the Soviet grain embargo the week Congress returned from its Easter recess so the action would help with farm state votes on both the budget and the farm bill. The decision was Reagan's. But the timing was largely his chief of staff's.

While they work well together, Meese, Baker and Deaver do not work alike.

Meese is management-oriented and likes to meet after the morning sessions with his own staff: Cabinet administrator Craig L. Fuller (who once worked for Deaver's public relations firm in California), deputy counselor Robert M. Garrick and assistant counselor Edwin W. Thomas Jr.

Baker's style is more one-on-one. He will talk to his deputy, Frank Hodsoll, his staff director, David R. Gergen, or his staff secretary, Richard Darman, as the need arises, and frequently. His style is invariably direct and his follow-through persistent without being aggravating, says Deaver.

"We have had differences of opinion, never serious, and I think one of the reasons is that each realizes that the other brings something that the others don't have, and we respect that about the person," says Deaver.

"Baker brings an organizational mind and someone who's very detail-oriented to the operation. Meese brings that ability to get everybody talking and being able to develop a consensus from all of his advisers . . . I think what I try to do is think in terms of the governor and the way things ought to go for him."

Since the shooting, Reagan has been taking it as easy as he can. He needs to nap in the afternoon, and both Nancy Reagan and Deaver have done everything they can to make sure the president gets the rest he needs to recuperate.

In practical terms, this has made the Triumvirate even more powerful. It means that Reagan leaves the Oval Office for the residence at midday and rarely returns to work the same day.

Before the shooting, the Big Three used to gather with the president for another half-hour meeting late in the afternoon. That meeting remains on the schedule, but is held only about half the time. Sometimes, Deaver or another member of the Triumvirate goes to the residence for a signature or a decision. But none of them bothers the president in the afternoons when it can be avoided.

Reagan is by inclination and experience a delegator, so he wasn't bothered all that much with detail even before he was wounded. Reagan's attention was focused on the economic recovery program, and his aides tried to compress other isues into presidential decision memos not longer than a page and a half.

Attempting to demonstrate how much Reagan was involved in the decision to send sophisticated reconnaisance equipment to Saudi Arabia, a senior White House official said Reagan sat through three hours of discussions on the controversial issue.

"That's a lot of time for a president," he said.

When Haldeman ran the Nixon White House and John D. Erlichman the Domestic Council, everyone wrote memos, some of which wound up as part of the bill of particulars against the president when the House Judiciary Committee was working on impeachment.

The Reagan White House, in contrast, is unlikely to become famous for its memos. In this, the Triumvirate reflects the style of the president, who likes to talk to people when something goes wrong rather than write them letters.

Neither Baker nor Deaver likes to write memos, and Meese, who writes more often, is sparing by most previous White House standards.

What the Triumvirate does is talk, on a more or less constant basis. When they write, it is often a question or a note on a paper someone else has written. Baker, in particular, likes to use little scraps of paper when it becomes necessary to write something down. But he usually decides that it is quicker just to pick up the telephone.

Meese, as befits a policy adviser, is a little more formal and reads more than his colleagues. An aide says he has never seen the counselor without a sheaf of papers in his hand.

"We've got to keep campaigning," Baker said soon after he became chief of staff. It was his way of saying that the White House had to keep up the pressure for the economic program, as if Reagan were still engaged in his election campaign. The phrase became a watchword in the White House. The preferred medium, as always, was television.

The press-conscious Triumvirate, like Reagan, combines personal friendliness with a cunning understanding of the media and how it operates. The guiding principle is that a potentially damaging story should be answered immediately.

Deputy press secretary Larry Speakes, who frequently changes signals when a hot-potato issue comes up, gets his guidance for the daily briefing at a late-morning meeting with Reagan in the Oval Office attended by the Triumvirate, Gergen and Max Friedersdorf, the assistant for congressional liaison. They aim to make news for the evening television shows and also to head off negative headlines.

The tactical approach is both offensive and defensive: to decide on a communication that will prove irrestible for the evening television newscasts as well as the morning newspapers, and to anticipate embarrassing press questions.

Baker, Meese and Deaver hold at least one other formal meeting near the end of the day, a 4:30 p.m. session in Baker's office with E. Pendleton James, head of the White House personnel office. "Both Jim and Mike hate to go to that meeting, and they make jokes about it all the time," says one White House aide.

It wasn't always this way. In the early months of the administration, the White House took so much pride in the pace of its appointments that Meese and Baker handed out compilations showing the Reagan administration far ahead of most of its predecessors.

No one is handing out lists these days. The process is way behind and the president has said the progress on appointments is the biggest disappointment of his first months in office.

Still, as a measure of their authority and attention to detail, Meese, Baker and Deaver continue to take this time each day to discuss jobs and applicants. Ronald Reagan signs the appointments and others freely advise, but it is the Triumvirate that does the hiring and firing.