President Reagan's second-term team, pursuing what chief of staff Donald T. Regan calls "the president's agenda," has brought both a harder ideological edge and a tidier corporate structure to the White House, senior administration officials say.

White House officials and Republican members of Congress who assessed the performance of Regan and his deputies after a month on the job agreed that the new team is more orderly, conservative and confrontational with Congress than the first-term team headed by James A. Baker III, who swapped jobs with Regan and became treasury secretary.

"Don sees himself as chief executive officer," said one high White House official. "He's used to being in charge and making decisions. He's analytical but willing to fight. Baker was the corporate lawyer who pulled in both sides and worked out a compromise. This is more of a hard-core group."

In the past few weeks, the White House under the new team has launched frontal assaults in Congress to push for the MX nuclear missile and aid to the "contra" rebels in Nicaragua. Early budget skirmishes have been hard-line, including the high-profile veto of farm credit legislation, and more confrontations on spending legislation seem to lie ahead.

The most ideological member of this team is former columnist Patrick J. Buchanan, new director of communications. Regan told a conservative audience a week ago that Buchanan "gives new meaning to the word hard-core."

Returning to the White House, where he once wrote speeches for Richard M. Nixon, Buchanan has earned the sobriquet "director of non-communications" from White House reporters because he has followed a practice, intially ordered by Regan, of not returning telephone calls from reporters.

But Buchanan, in the words of an associate, also has put "starch in the pants of the rhetoric." On issues ranging from the farm bill to Nicaragua he has been a forceful advocate of Reagan's new combativeness with Congress. Buchanan's approach has upset some moderates, notably Reagan's longtime intimate, deputy chief of staff Michael K. Deaver, who is scheduled to leave the White House in May to join a Washington public relations firm.

Sources said that Deaver, the surviving member of an original staff trio that also included Baker and Attorney General Edwin Meese III, bluntly told Buchanan he was "too ideological." Buchanan, whose columns were critical of Baker, Deaver and sometimes of the president, reportedly replied that he would be a team player.

In an interview in his office Friday, Regan agreed that the White House has embarked on a more conservative course but said this suited the president's "determination" to complete what he started in the first four years.

"We're not here to make our own agenda," Regan said. "We have a team that will carry out what coach says are the plays . . . . He's going to call the plays, and we're going to execute them."

Regan's defense -- that he is doing what the president wants -- is identical to the one made during the first term by Baker and presidential assistant Richard Darman when they were accused of moderating Reagan's policies.

As governor of California and as president, Reagan has prided himself both on adherence to ideological principle and on an ability to negotiate and compromise. The "plays" he calls usually have been general guidelines subject to widely varying interpretations by different managers and strategists.

The new team's tendency toward confrontation, while pleasing to conservatives, worries some congressional supporters.

One veteran Republican House member, who has backed the president on every major policy initiative, complained last week that the White House staff "talks a tough line but hadn't really focused on the budget and the difficult decisions we face."

A White House official, echoing this concern, said it is necessary for Reagan to demonstrate his willingness to veto "budget-busting bills," such as the farm credit measure, but that it also is important that he display "compassion and a willingness to compromise."

One sign of the administration's rightward drift is that Edward J. Rollins, the presidential political assistant who was considered a conservative in the first term, now is viewed as a "pragmatist." Some would apply the same label to Max L. Friedersdorf, the legislative strategist who has served in three Republican administrations.

Regan relies heavily on Friedersdorf's advice in dealing with Congress. Last week, for instance, the White House had planned a veto of the farm bill the day after it passed Congress. But Friedersdorf called legislative leaders and was told that many members would be absent the next day and that an immediate veto would send a stronger signal.

As a result, the president delivered a stinging veto message the afternoon the bill was sent to him.

The other senior member of the Regan team is policy assistant John A. Svahn, a holdover with close ties to Meese.

When Regan took over as chief of staff, it was expected that his Cabinet secretary and longtime associate Alfred H. Kingon would gradually eclipse Svahn. But Kingon, described by one aide as "uneasy in his new role," has found that Svahn, with firm alliances in the Cabinet, is not easy to displace.

Personal and policy feuds were commonplace in the White House during Reagan's first term. Often, as factions took their case to the public, they resulted in the news "leaks" that are abhored by the president.

While Reagan often complained about "leaks," he rarely seemed to recognize that the organizational structure he had approved encouraged them. Baker, often allied with Deaver, frequently was at odds with Meese, who was then presidential counselor. For a time, when longtime Reaganite William P. Clark was national security affairs adviser, he and Baker were rivals.

Baker's departure to Treasury has been a blessing for William J. Casey, the once-embattled director of the Central Intelligence Agency, who also has told intimates he will be happy when Deaver departs.

Casey reportedly believed that he was blamed by Baker and Deaver for the congressional revolt against the administration's attempt to aid anti-Sandinista rebels in Nicaragua. After a CIA-backed scheme to mine Nicaraguan harbors became a political embarrassment last year, Congress cut off funds to the rebels, and Casey became nearly invisible during the presidential campaign.

Now, Casey is said to be pleased with the Regan team and with the unyielding line that the president and Secretary of State George P. Shultz have taken in seeking financial aid for the rebels they call "freedom fighters."

In reorganizing the staff, the new chief of staff has been guided by his corporate experience and the absence of a serious leadership rival. Punctual and well-organized, Regan also delegates freely. He said he learned this on Wall Street, where he told subordinates, "If I'm going to do your job, I want your salary as well."

Regan normally breakfasts with Deaver and one or two close aides at 7:30 a.m. and gathers at 8 a.m. with his senior staff. Those who attend the meetings say they are businesslike, but that Regan welcomes frank differences of opinion on issues and strategy.

Afterward, Regan meets privately with the president and sees him from time to time during the day. Unlike Baker, who was apt to barge into any office on a moment's notice, Regan works quietly in his office with the door closed. He usually leaves by 6:30 p.m.

His style totally contrasts with Baker's.

"Jim was his own legislative relations director. He would call back every member of Congress," an aide said. "He was his own press secretary and would make calls to reporters without telling anyone. He was a consummate politician. Don Regan is a manager."

Regan frequently contrasts his new job with his old one by saying that Treasury was "an eyes job" in which he obtained most of his information by reading. He says that being White House chief of staff is "an ears job" where one is constantly besieged by phone calls and requests and where little time remains to read lengthy documents.

When Regan became chief of staff last month, it was widely thought that he would be less accessible than Baker and that he was something of a "yes man" who would be reluctant to bring the president bad news.

He has surprised people on both counts. Regan, who has kept White House spokesman Larry Speakes well-informed and given him a vote of confidence, has set aside a half hour each day to meet with reporters whom Speakes designates.

The new chief of staff bristles at the "yes man" label and tried to demonstrate that he does not deserve it. Last week he was the first to tell Reagan that Deaver and other aides on a European advance trip had used their diplomatic passports and purchased German automobiles at substantial discounts.

The presidential response, according to an official, was "an expletive which for your family newspaper should be written as 'Shucks.' "

But the infighting that was conspicuous during the first Reagan term has not disappeared under the new chief of staff.

Buchanan, whom Regan calls a "communications planner," has been in a polite conflict with Rollins over who will control the 36 slots in the Office of Public Liaison when its director, Faith Ryan Whittlesey, returns to being ambassador to Switzerland. Last week the two men worked out a division of the office, but Regan has as yet declined to approve it. Even while trying to play a low-visibility role, pending the departure of Deaver, Buchanan has been something of a storm center within the administration and a lightning rod for conservative causes. When a conservative radio announcer reported that a moderate Republican legislator would replace Whittlesey, his remedy was to encourage listeners to call Buchanan.

The calls completely tied up Buchanan's switchboard, causing him to complain, "I'm trying to get Jack Svahn on the phone, and I can't even get a dial tone."

Buchanan's dealings with reporters have been limited to calls to a couple of old acquaintances, one of whom had written a profile about him. "Your income taxes aren't in all that good shape," Buchanan said, a comment that the reporter took as a joke.

Buchanan's greatest impact has been on speechwriting, the one department securely under his jurisdiction. Reagan's speechwriters always have been conservative, but they sometimes toned down their drafts to win the approval of Darman or Buchanan's moderate predecessor, David R. Gergen.

"The danger is that to the outside world Reagan is what he says," one White House official said. "The speechwriting group was trying to write down for Gergen and Darman. Now they're trying to write up for Buchanan."

The result has been more combative speeches, although Buchanan has not always had his way. A reference to the Sandinistas as "thugs" was deleted from a speech Reagan gave to the Conservative Political Action Conference, and objections from national security officials muted some of the harshest anti-Soviet statements in the original draft.

Both Buchanan's boosters and detractors praise his energy and commitment, and expect him to gain influence after Deaver departs.

"Pat doesn't define communications the way it was defined by Gergen or the way it is defined by the press corps," one official said. "He thinks his tool is the president, and he wants to make policy."

Key Hill Republicans and holdovers in the White House have been reluctant to pass quick judgment on the new White House team. Many like Regan and admire his forcefulness and openness while questioning his long-distance political skills.

Even some conservative officials say they think that the White House team may have been hurt by the departure to Treasury of Darman, who skillfully directed long-term legislative strategy.

Others predict that Regan, who has formed a close bond with the president and has the good will of Nancy Reagan, will prove to be precisely the kind of combative and authoritative chief of staff that Reagan needs to force through his second-term agenda.

"Being confrontational with Congress may be a necessary tactic to get out of the mire we're in during the next 90 days," one official said. "Baker would be up there negotiating. The risk of doing it Regan's way is that we may get nothing."

Another Republican close to the administration thinks that the Regan team has made a good start but remains untested.

"We won't know how good they are until a real crisis occurs," a Republican close to the administration said. "Then we'll know in a hurry."