After almost 10 months in office, Secretary of State Alexander M. Haig Jr. has decided on a modest revamping of his high command, including shifting Myer Rashish out of his present post as undersecretary for economic affairs, according to several administration sources.

These sources say Haig wants to replace Rashish by promoting Robert D. Hormats, currently an assistant secretary of state for economic and business affairs. But this has not yet been cleared at the White House.

There have been other recent tremors at the top of Haig's State Department hierarchy, according to these sources. Haig is said to have moved in recent days to replace John H. Holdridge, assistant secretary for East Asian affairs, but then reversed himself and assured Holdridge that the job remains his.

"John Holdridge's job is as secure as any job at State," said one top-level administration official, who meant to be reassuring while acknowledging the changes that had occurred.

In a move relating to the conduct of U.S. diplomacy outside the State Department, sources say National Security Council staff member James R. Lilley will be named director of the American Institute of Taiwan.

The institute has served as a substitute for an embassy since the United States formally broke governmental relations with Taiwan in 1979 after recognizing the People's Republic of China.

Lilley spent 27 years with the Central Intelligence Agency, becoming the agency's top expert on China, and also served in Beijing (as did Holdridge) when George Bush headed the liaison office there.

Haig has also decided, according to sources, to fill two controversial posts that have remained vacant since Inauguration Day: assistant secretary for human rights and the director of the bureau for refugee programs. Announcement of these appointments will be made shortly, the sources said.

Although he is replacing Rashish as his top economic policy official, Haig is said to be considering nominating Rashish to be secretary general of the European-based Organization for Economic Cooperation and Development.

Administration and State Department sources gave differing explanations for the replacement of Rashish and, to a lesser extent, the episode with Holdridge. In the case of Rashish, Haig was said by some sources to be dissatisfied with what he considered to be delays in the delivering of preparatory paperwork for the seven-nation summit meeting in Ottawa last July and--most recently--the forthcoming 22-nation, North-South summit meeting in Cancun, Mexico.

In the case of Holdridge, Haig was said to be unhappy with the handling of certain aspects of his recent trip to China. But both cases, several sources say, reflect differences in operating style between Haig and these two subordinates.

For example, Haig and several other senior officials are known to have felt that the State Department needed a more vigorous representation in the administration's interagency economic discussions. Rashish was professionally respected, one source said, but Haig wanted "someone more bureaucratically skillfull and vigorous internally . . . at playing the game."

These sources stressed that Rashish's job was not an easy one and that there are powerful forces in other agencies, such as the Departments of Treasury and Agriculture, on trade policy questions.

But the State Department has not done well on a number of issues such as trying to hold down White House-approved grain sales to the Soviet Union or convince West Europeans that they shouldn't build a gas pipeline to Russia. Some State Department officials feel that these policies are in sharp contrast to other administration rhetoric that challenges Moscow on the defense and foreign policy fronts and thus sends confusing signals abroad over American foreign policy.

Other senior officials said that Rashish, while perhaps not a strong bureacratic infighter, provided the secretary with sound economic policy advice. Another official added that Rashish is "a Reaganaut," loyal to President Reagan and his policies.

Haig had talked recently to Holdridge about shifting him into an ambassadorial job, sources said. But Haig changed his mind and informed Holdridge that he would remain the department's senior policy adviser for Pacific and East Asian affairs.

Haig's displeasure with Rashish and Holdridge became an open secret after the secretary was said to have erupted in harsh criticism of the two at a meeting of top staff advisers in August. Word of Haig's comments at the meeting, which occurred while Rashish was on vacation, was circulated throughout the top floors of the State Department.

At that meeting, according to sources, Haig criticized Holdridge's handling of the secretary's visit to China. He also criticized Rashish for comments in an interview with The New York Times on how a global policy of wealth redistribution was not possible, but a policy of "wealth creation" was the administration's goal.

Just before leaving on vacation, Rashish has told friends, he received a message from Haig praising him for comments in the interview.