The still-young Reagan administration is struggling to rid its national security apparatus of disarray caused by uncertainty over who is in charge, by a few ill-chosen statements and by Washington's traditional turf fights at the top over territorial imperatives.

Partly in an effort to bring harmony to the Reagan high command, it has been decided that Vice President Bush will be placed in charge of a new structure for national security crisis management, according to senior presidential assistants. This assignment will amount to an unprecedented role for a vice president in modern times. In the Carter administration, the crisis management structure was chaired by Zbigniew Brzezinski, the national security adviser.

Also, top-ranked White House aides have taken direct control over the responsibility for coordinating the policy preparation of the president for foreign trips. The action came after President Reagan and his senior assistants were dissatisfied with the way the State Department handled the preparation for Reagan's recent visit to Canada, White House officials said.

"I'm not sure we're at the end of this," said one knowledgeable Reagan official. "The process is still evolving."

Disarray and disputes in national security decision-making are by no means unique to the Reagan administration. Similar problems plagued former president Carter throughout most of his four years and became a campaign issue upon which Reagan built himself a new foundation of political capital. Reagan officials boasted that they were going to "hit the ground running" and "speak with one voice."

Instead, many of the same officials have viewed with displeasure and dismay those administration policy pronouncements that have all too often appeared in public to be a two-step process: declaration and disavowal.

The White House, for instance, recently rejected a State Department official's remarks on El Salvador and the press, and also disavowed a National Security Council staff member's extreme assertions on the Soviets and detente. Before that, there were rollbacks of such statements as the defense secretary on neutron warheads and the secretary of the Navy on the strategic arms limitation treaty.

On a broader, policy-making level, senior White House officials were unhappy with what they felt to be ill-timed and ill-considered actions by Secretary of State Alexander M. Haig Jr. that placed the brightest spotlight on El Salvador at a time when the administration was trying to focus maximum attention on Reagan's economic proposals.

They said that Reagan's senior White House aides had not approved in advance Haig's decision to send a well-publicized memo to U.S. allies detailing the extent of communist arms shipments that were represented as being funneled to the guerrillas in El Salvador, nor the sending of Haig's assistant secretary of state-designate for European affairs, Lawrence Eagleburger, to inform the European allies personally of U.S. concern over the arming of these rebels.

Most recently, just after White House officials felt they finally devised a structure for the making of national security policy decisions, they found themselves locked in intramural intrigue over a decision on whether to postpone a scheduled meeting with the Soviets on SALT -- a dispute that symbolizes the confusion among the secretary of state and the president's national security adviser.

One major unresolved issue is the ultimate influence to be wielded by the NSC staff, headed by Richard V. Allen. "The role of the National Security Council is under intense debate," said one senior White House official.

The latest White House move to take control of the policy preparation for presidential trips does not necessarily mean a greater role for the NSC staff, however. Coordination will be supervised by Michael Deaver, deputy chief of staff, assisted by aides representing presidential counselor Edwin Meese III and chief of staff James A. Baker III.

The NSC staff will work along with State Department officials in compiling policy position papers that will be submitted through these other White House assistants. In recent administrations, by contrast, the national security adviser took the lead role in coordinating policy matters for presidential trips.

The problem with the State Department's handling of the Canada trip was that too much material was given Reagan at the last minute, and far too little consultation was done with such senior officials as Commerce Secretary Malcolm Baldridge and trade representative Bill Brock, White House sources said.

Deaver has already begun coordinating the upcoming Reagan trip to Mexico. The concerned departments and agencies have already been asked to provide their policy position papers, which Deaver says places the administration well ahead of the pace for the Canada trip.

The vice president has been asked to coordinate one upcoming trip, the summertime summit on economic matters that will be held in Ottawa and will be attended by Reagan and major U.S. allies.

Bush was chosen in part to smooth the concerned feelings over the consultation for the first Canada trip, officials said. "We thought the vice president, being who he is, could bridge that with the greatest degree of authority," said one official.

Bush's stature, by virtue of job title and experience, was cited as the reason that he was chosen to chair meetings in the Situation Room in time of crisis. Principal officials involved in crisis management will be the secretaries of state and defense, the Central Intelligence Agency director, the national security adviser, Meese and Baker, officials said, adding that the structure has not been fully devised nor the presidential directive written.

Reagan officials emphasized that Bush, a former director of the CIA and former United Nations ambassador, would be able to preserve White House control over crisis management without irritating Haig, who they stressed was probably the most experienced and able of all other officials who could serve in that function.

"The reason for this [the choice of Bush] is that the secretary of state might wish he were chairing the crisis management structure," said one Reagan official, "but it is pretty hard to argue with the vice president being in charge."

Presidential national security adviser Allen -- partly at his own initiative, and partly because of Haig's formidable credentials -- has assumed a low-key role in the administration's policy-making hierarchy.

There are some administration officials, particularly inside the NSC staff, who would like to see Allen be more assertive and feel he is adrift and abdicating a leadership role. But Allen, who is held in high regard by the president and his inner circle for his loyalty to Reagan and for his collegial ways, has maintained privately that he is confident that over the long run his influence and that of his staff will be sizable in the shaping of national security policy.

The issue that thus far best typifies the problems in the national security area is the dispute over the scheduled SALT session in Geneva this week. It began with Allen making an effort to assert authority.

In late February, Baker and Meese, with the blessings of the president, approved a national security policy decision structure that called for the creation of three senior interdepartment groups (SIGs), chaired by the secretaries of state and defense and the Cia director.

The framework called for issues to be assigned to the various committees by White House coordinators, Allen and his boss, Meese, according to several presidential assistants.

In what proved to be an early test of the new collegiality, Allen -- acting on his own -- sent a letter to Defense Secretary Caspar W. Weinberger asking the Defense Department to chair a meeting to decide whether the United States should go to the long-scheduled March 25 meeting with the Soviets in Geneva, a SALT compliance and review arm known as the Standing Consultative Commission.

But Weinberger did not respond to Allen's note. Instead, eventually, Deputy Secretary of Defense Frank Carlucci and Deputy Secretary of State William Clark sent Allen a cool note -- one White House official calls it "snotty" -- saying that the matter was already under review and that when the president needed to be informed, the president (apparently instead of Allen) would be informed.

Some administration officials believe that Allen had sent his request to Weinberger mainly because he was eager to give someone other than Haig the role of chairing the question, even though these officials say, SALT has traditionally been viewed as more of a political and foreign policy issue than a military one.

Allen says this was not his motive at all. But he candidly adds that, "in retrospect" he should have written a memo to Weinberger and Haig asking them to get together and review the matter "because that would have avoided misunderstandings."

The issue proved one of internal controversy. Haig and Weinberger favored a postponement of the Geneva session until the administration could formulate a comprehensive strategic policy. Allen favored going ahead with the Geneva meeting, and using the session as a forum for attacking the Soviets for what some administration officials say have been numerous violations of existing SALT accords. Allen's view wound up being supported by the Joint Chiefs of Staff and by the State Department's Arms Control and Disarmament Agency.

But Haig and Weinberger apparently sought to end the issue before it could become an intra-administration debate. State Department official Richard Burt convened an intergovernmental group on the issue but began the March 4 session by announcing that Haig and Weinberger had just decided over breakfast that morning to postpone the Geneva session. An account of this much of the controversy was first made public by syndicated columnists Rowland Evans and Robert Novak.

What happened next is a demonstration of how power policy-making sometimes operates at the top. Haig sent a "decision memorandum" to the president on the issue. The document was signed only by him and reflected only the arguments in favor of postponing the Geneva meeting, sources said.

But the document then was given to Reagan in a meeting attended by Allen, Baker, Meese and Clark. At that session, Allen and his White House colleagues laid out the arguments for going ahead with the Geneva session on schedule, including the points that a postponement could be viewed with alarm abroad by European allies and at home by liberals.

Reagan sided with Haig and Weinberger, agreeing to postpone the Geneva session for about a month.

But then, apparently to demonstrate for posterity a unanimity within, it was decided that an entirely new decision memorandum should be written and submitted to the president. This one was actually two memos in one. The first part was written by Haig; it recommended postponing the Geneva session and listed the reasons why. The second part was written by Allen; it gave the arguments against postponing the SALT session -- but then recommended that on balance it probably should be postponed after all.

The decision-making process proved in this case to be haphazard, perhaps because the various major players were eager in this early foray to stake out their territorial imperatives. But Reagan officials were taking comfort last week that at least all the job finally got done.

"Well, it didn't happen by the book," conceded one senior administration official. "It didn't happen the way we'd like it to happen. But the point is that the president is the one who made the final decision, and he did that after eventually reviewing all of the options."

But even with this decision made, new arms control battlelines are being drawn in the Reagan inner circle. To avoid these sort of problems of politics and policy and turf, the White House is seeking to take the reins on this issue, too.

Said one White House official: "We've agreed here that from now on, arms control matters have to be chaired centrally and not just handed over to one department or another." Baker and Meese have agreed to this, according to the official. But this does not mean that Allen, who as national security advisor would seem heir apparent to the chair, will actually be put in charge of coordinating arms control matters.

"That has not been sorted out yet," the official said. "We're still getting it together. Haig is still a very strong player -- the preeminent player. There's a reluctance to rein him in. But I think eventually this will lead to greater control from within the White House and the NSC staff. Events will lead to this because State just can't formulate a presidential perspective -- one that takes into account the many domestic, economic, political and other points of view.

"Al Haig, good as he is, is just not in that loop."