Secretary of State George P. Shultz, as part of a new effort to work out a politically acceptable system for increasing sales of U.S. nuclear technology abroad, yesterday shifted Richard T. Kennedy, under secretary for management, to a new position in charge of nuclear nonproliferation and energy matters.

Kennedy, who will have the title of ambassador at large, had been exercising de facto control over the State Department's nuclear policy functions since last March, when then-secretary Alexander M. Haig Jr. took that responsibility away from James L. Malone, the assistant secretary for scientific affairs.

In fact, Kennedy's preoccupation with nuclear policy and his position as U.S. representative to the International Atomic Energy Agency are known to have caused complaints within the department that he was neglecting the management, personnel and administrative functions of the under secretary's job.

By creating the new position and replacing Kennedy as under secretary with Jerome W. Van Gorkam, a Chicago businessman, Shultz appeared to be moving both to tighten up the department's internal management and to sort out nuclear policy, finding some palatable way of reversing the restrictive nuclear-export policy in effect since the Carter administration.

Carter, whose views are still shared by powerful elements of Congress, looked askance at such exports on grounds that they would help more countries build nuclear weapons. President Reagan has argued, on the contrary, that increased sales will increase U.S. influence with other governments.

Malone, who originally was supposed to work out the policy shift, suffered a severe blow last year when it was reported that he intended to propose giving the State Department almost unfettered authority to license foreign nuclear sales without restraint by Congress or the Nuclear Regulatory Commission.

These proposals were denounced by congressional critics as a total reversal of past efforts to prevent the spread of nuclear weaponry, and congressional sources say that the residue of suspicion on Capitol Hill made it virtually impossible for Malone to work with Congress on possible compromises.

In March, Haig sought to shift Malone to ambassador at large for Law of the Sea negotiations, but that plan was dropped when conflict-of-interest questions impeded Malone's confirmation by the Senate. He since has gone back to the assistant secretary post, but the nuclear policy functions within Malone's bureau of oceans and international environmental and scientific affairs have remained under the control of Kennedy, a former NRC member.

In that capacity, Kennedy has shown himself to be a staunch advocate of the Reagan approach on proliferation questions, and Shultz, who personally announced the appointments at the department's daily press briefing, said he had "great expectations" that Kennedy will bring the president's policy to fruition.

However, the amount of time Kennedy spent on nuclear matters is known to have irritated department officials and rank-and-file members of the foreign service, who charge that he has not given proper attention to personnel and budgetary matters. Last year, the American Foreign Service Association, which includes more than 7,000 active-duty and retired foreign service officers, informed Kennedy by letter of its concern over his attempt to do two jobs.

Van Gorkam is an attorney and businessman who most recently has been chief executive officer of Trans Union Corp. in Chicago. He also headed a special citizens' committee that sought to resolve some of the problems besetting the Chicago public school system.