President Reagan's top assistants, back from their August vacations, have begun a modest revamping of the White House staff that includes the departure of several mid-level aides.

Most of the changes center around the press and communications officials who report to director of communications David R. Gergen, according to presidential aides. These changes will likely be announced next week.

Deputy press secretary Karna Small, one of the few women in higher echelon jobs in the Reagan White House, will be shifted out of her present post, according to White House officials. She will be offered another job, they said, perhaps one involving extensive out-of-town speaking assignments, which would make use of her experience as a television news personality.

Also, Reagan's senior assistants plan to merge the White House communications office, which coordinates press operations within the executive branch agencies, and the White House media liaison office, which handles requests from out-of-town journalists. They will be combined into a single, streamlined office, these sources said.

Frank Ursomarso left Tuesday as director of the communications office, and has returned to Delaware to run his family's car dealership. Louis E. Gerig will likely be shifted out as head of media liaison, according to White House officials. There was no word yesterday as to whether he will be offered another post. Officials said, however, that Michael Baroody, an aide in the present communications office, will have a greater role in the new, combined operation.

The plan to streamline the communications and media liaison operations was proposed to Gergen and White House chief of staff James A. Baker III in a report by Peter Roussel of Houston, who had been hired by the Reagan White House to do a two-month study of the press and communications operation, according to presidential aides. Roussel, who has worked as an aide to Baker and Vice President Bush in years past, will join the White House staff as a deputy press secretary. He will be involved primarily with administrative duties, sources said.

Job shifts also are expected for deputies to Baker and White House counselor Edwin Meese III. Baker's deputy, Frank Hodsoll, is expected to be named director of the National Endowment for the Arts, White House sources said.

It is unclear whether Robert M. Garrick, a retired admiral who has served as Meese's press contact, will have a new job within the administration or return to his job as senior vice president of a public relations firm in California.

Meanwhile, Baker and Gergen are actively involved in the search for a chief speechwriter. Reagan, heralded for his abilities at public communication, has operated for months without one.

Several persons outside the White House staff, including former Washington Star editorial writer Anne Crutcher, have been interviewed for the job, sources said. One current White House speechwriter, Anthony R. Dolan, is a contender, the sources said. But they added that senior White House officials are considering hiring a more experienced person to serve as an "executive editor" of the speechwriting staff, with Dolan serving as chief writer.

Baker and other White House advisers are said to have made no decision on the political affairs office if its present chief, longtime Reagan adviser Lyn Nofziger, resigns at the end of the year, as he has often said he will.

Baker has said privately that he hopes to persuade Nofziger to stay on the White House staff through the 1982 election. Nofziger is known to feel that he has not been involved often enough in major decisions. He also wanted to be in charge of White House communications, the job that eventually went to Gergen, sources said.

Senior White House officials said that, contrary to published reports, there are no plans to shift Richard S. Williamson, Reagan's liaison official for state and local government, to the political affairs job if Nofziger leaves.

The political office may be abolished, leaving the function mainly to the Republican National Committee, some White House officials said. But others said Baker prefers to keep the political office operating in the White House.

One of Nofziger's deputies, Edward Rollins, is considering an offer to become campaign director for California Lt. Gov. Mike Curb's gubernatorial campaign and may leave the Nofziger shop before his boss departs.