Senior State Department officials insist that it is nothing more than the normal personnel reshuffle at the start of a new presidential term. But Secretary of State George P. Shultz's plan to put a number of new faces in key embassy and policy posts is threatening to cause a major challenge from conservatives who suspect he is trying to gain total control over the administration's foreign policy machinery.

At issue is a projected series of changes that would install new ambassadors in about one-third of U.S. embassies. It also would enable Shultz to replace roughly four to six officials at the assistant secretary level, most of them political appointees inherited when he took office 2 1/2 years ago.

The big question is whether the conservative challenge can gather enough steam to force Shultz into abandoning this ambitious round of musical chairs within the State Department. Whatever the outcome, Shultz seems destined to be marked by conservatives as an adversary.

After meeting with Shultz Friday, President Reagan appeared to come down on the secretary's side. When reporters asked about complaints that Shultz is "stacking the State Department with moderates," the president replied:

"I have read all of that and, no, it is not true. He and I have met and discussed all of the changes that are being made and most of these are just rotations. The individuals are going from one place to another. It just isn't true . . . . There's a limit to how long you prefer to leave, particularly the career ambassadors in one . . . place."

White House officials said the president's answer was in line with his usual approach of delegating considerable authority to his principal Cabinet officers and avoiding becoming involved in how they run their departments.

As a result, these officials said, it would be highly uncharacteristic for Reagan to countermand what are essentially middle-level personnel decisions. However, the officials also said that if the groundswell of conservative anger continues to build, the president could be confronted with a new ideological battle between the conservative and pragmatic wings of his administration.

In discussing the shifts last week, department spokesman John Hughes denied that the changes have any ideological motivation. He insisted that Shultz's "primary criterion . . . is getting the best possible people to carry out the implementation of the president's foreign policy."

But, in the view of conservatives, the secretary's real purpose is not to implement the hard-line policy stances on which Reagan twice campaigned successfully for the presidency but to bring them more into line with the views of those administration moderates with whom Shultz is identified.

In particular, the conservatives suspect the so-called Shultz faction of maneuvering to soften Reagan's approaches to arms control and the threat of communist penetration in Central America.

As a result, they have been complaining privately to the White House that Shultz's real aim is to change not personnel but policies, by purging the State Department of political appointees ideologically attuned to the president's wishes and replacing them with career Foreign Service officers who have no special loyalty to Reagan and are more susceptible to the secretary's control.

The charges and denials have left a cloud of confusion. But conservatives clearly perceive important ideological issues at stake.

The controversy first broke into public view on Dec. 11 as Shultz was leaving to attend the NATO meeting in Brussels. On that day, syndicated columnist Joseph Kraft published an article saying that Shultz intended to control foreign policy with "professionals in the State Department -- not superstars from outside."

Kraft detailed areas where Shultz allegedly is determined to have his own people in charge. They ranged from such top-priority subjects as arms control and the Middle East down through obscure corners of State Department business and even included a list of assistant secretaries who "came to State from competing power bases" and who, Kraft concluded, were "good bets . . . to be leaving soon."

The people he mentioned as ripe for being purged are largely unknown outside the department and foreign policy circles. But they shared the common bond of identification as staunch conservatives, and the Kraft column thus touched off a firestorm among like-minded figures in the administration and Congress.

In the ensuing days, while Shultz was in Europe, a counterattack was mounted through private calls to the White House and a public recourse to the press. Monday, a week after the Kraft report appeared, Rowland Evans and Robert Novak, whose syndicated column is a popular outlet for conservative-inspired leaks, wrote that Shultz, egged on by young Foreign Service officers, was purging Reaganites with a vehemence intended to make clear "that outsiders are no longer welcome at the State Department."

"With Shultz now in the close embrace of the Foreign Service, the president's diplomacy is likely to be turned away from his own strong ideological convictions on the world struggle," Evans and Novak concluded. Conservatives have since been making abundantly clear to other reporters their conviction that the ideological soul of the administration's foreign policy is at stake.

"This was a purge from top to bottom, not a normal personnel switch," said one important administration conservative in reference to what his allies are calling "the Christmas massacre." He added, "The impact of these moves would be to change policy in Central America by putting in moderates who are opposed to the president's policy and who would undercut it."

This source said that in the past week "there have been lots of calls in protest from personal friends of the president and from congressmen and senators." Among those who have been most vehement in their protests, he said, were Sen. Jesse Helms (R-N.C.), the dean of Senate conservatives, and Rep. Jack Kemp (R-N.Y.), the ranking minority member of the House appropriations subcommittee that deals with foreign aid.

An aide to Kemp confirmed that "Jack has let the White House know that he has significant problems with this." The aide said Kemp was disturbed by the "entire panoply of the changes." As examples he cited Shultz's intention to replace James Theberge, the ambassador to Chile, who advocates coaxing the military government there toward democratization through friendship rather than confrontation, and John D. Negroponte, who is slated to be supplanted in the Honduras embassy by L. Craig Johnstone, deputy assistant secretary in charge of Central American affairs.

Kemp "sees people who have loyally followed Ronald Reagan's policies being summarily dismissed and replaced by others who do not support those policies. So he can only conclude that Shultz has decided to engineer a shift of our policy in Central America," Kemp's aide said.

Such charges have caused both consternation and bemusement at the State Department, where senior officials scoff at the suggestion that Shultz is masterminding a surreptitious plot to delude Reagan into changing his foreign policy. While acknowledging that Shultz "intends to be in command of his personnel situation," they insist that the shifts have no purpose other than what has been stated publicly -- more effective implementation of Reagan policy.

According to department officials, the changes involving ambassadors result from a number of considerations, including a plan proposed several months ago by Ronald I. Spiers, undersecretary for management, for more systematic rotation at three-year intervals of the heads of missions abroad.

Ambassadorial changes will be made because some individuals have requested new assignments, some have been in their posts for several years and some are serving in countries where local circumstances, such as changes in the political climate, make it advisable for the United States to be represented by a fresh face, officials said.

That, they noted, is the situation in Chile, where mounting discontent with President Augusto Pinochet's government is causing the administration to reassess the policies with which Theberge has been associated.

Regarding Honduras, the officials pointed out that Negroponte has served almost four years in what is regarded as a hardship post and, far from being cast aside, is slated to become an assistant secretary.

The contentkon that his tentatively designated successor, Johnstone, is being sent to Honduras to change policy evokes angry denials from department officials. They point out that Johnstone, as the operating boss in Washington of Central America activities, has been closely associated with the same policies for which the conservatives praise Negroponte and has been criticized frequently by liberals as an apologist for administration policy.

Department officials also insist that Shultz's decision to get rid of some political appointees was based not on their ideological convictions but on his feeling that they aren't doing their jobs satisfactorily. By contrast, they noted, several other political appointees with strong conservative credentials, among them William Schneider, undersecretary for security affairs, and Edward J. Derwinski, the counselor of the department, are given high marks by Shultz and remain firmly entrenched.

In hindsight, some department officials say the timing of the proposed personnel changes was unfortunate. It comes when the probable departure of such hard-liners as U.N. Ambassador Jeane J. Kirkpatrick and counselor Edwin Meese III will make it more difficult for those conservatives who remain, such as Defense Secretary Caspar W. Weinberger and CIA Director William J. Casey, to influence White House policy.

Shultz's recent success in having Paul A. Nitze chosen as his special adviser for the upcoming talks with the Soviet Union on arms control is widely regarded in conservative circles as the first signal of their waning influence. They regard Nitze as a Shultz agent, responsible to the State Department.

Shultz's essentially apolitical and pragmatic approach to choosing subordinates does not leave room for an ideological litmus test in making appointments. He has shown a preference for bright young officers from the career Foreign Service and trusted old cronies from the academic world.

"Shultz's predilection is for people with a great deal of expertise in their subjects, people who can staff a problem, give him all the pros and cons of the various options for a solution and, once he's decided on a course, go back and implement it," one department official noted. "He doesn't ask if they're Republicans or Democrats or who they voted for in the last election. He figures that ultimately it's him, not his subordinates, who has responsibility for ensuring that what's done conforms to the president's wishes."

Given the convergence of all these factors, it probably was inevitable that conservatives would see the personnel reshuffle as a sinister grand design. And, some White House officials say privately, the State Department compounded the problem by not showing sensitivity toward conservative concerns.

During Shultz's absence in Europe, the officials say, Deputy Secretary Kenneth W. Dam did not consult and reassure those in the White House and Congress who were most likely to be concerned. The result was a barrage of conservative criticism.

Since then, Shultz has moved swiftly to repair the damage. In addition to meeting with Reagan, he talked at length with Sen. Richard G. Lugar (R-Ind.), incoming chairman of the Senate Foreign Relations Committee, to assure him that the personnel changes will not mean changes in policy. Lugar's support could be critical if conservatives like Helms, the committee's second-ranking Republican, try to use the Senate confirmation process to obstruct new appointees.

Some administration sources said Shultz also might find it expedient to soothe conservative anger by making a tactical retreat on some of the proposed personnel changes. But, the sources added, it seems unlikely that Reagan will risk undermining Shultz's authority on the eve of his Geneva meeting with Soviet Foreign Minister Andrei A. Gromyko. Instead, they suggest that conservatives who are furious with the secretary will have to wait for a more opportune moment to try to rein in his authority.