WASHINGTON (AP) _ Some career officials and even some Reagan administration appointees have expressed wariness about the professionalism and ideology of the people that Attorney General Edwin Meese III will bring into the Justice Department.

But in his first week on the job, the former presidential counselor moved, during a series of face-to-face meetings, to allay those fears with affability, humor and promises of continuity.

He impressed many as ''personable and easy to work with,'' in the words of one official, and persuaded some doubters to withhold judgment about his appointees until they are chosen.

The department's No. 3 official, Associate Attorney General Lowell Jensen, who has been briefing the new attorney general, says Meese's first priority will be to fill vacancies. Jensen was once Meese's boss in the Alameda County, Calif., district attorney's office.

Deputy Attorney General Carol Dinkins leaves Tuesday. Francis Mullen, head of the Drug Enforcement Adminstration, has resigned. Antitrust chief J. Paul McGrath leaves April 1, and five of the 11 assistant attorneys general are serving on an acting basis. Thirteen out of 52 deputy assistant attorney general posts are vacant.

Such concerns do not lie only with those who opposed Meese's nomination as attorney general, but apparently extend as well to his Justice Department precedessor, William French Smith. Several of Smith's top aides said Smith had disparaged Meese's deputies as ''the most incompetent and least able'' imaginable. These aides, like others interviewed for this story, agreed to speak candidly only on condition that they not be quoted by name.

Early in the first term, Jensen's predecessor, Rudolph Guiliani, abruptly shooed away a Meese protege, Louis Guiffrida, who wanted to transfer authority for thwarting domestic terrorism from the FBI to the Federal Emergency Management Agency, which he heads.

Another Meese protege, Immigration Commissioner Alan Nelson, who worked with Meese in the Alameda prosecutor's office, once made a proposal that raised eyebrows during a discussion of what to do with unwanted Cuban refugees from the Mariel boatlift, according to an official who was there.

He said Nelson called for organizing the Cubans into an expeditionary military unit patterned on the movie, ''The Dirty Dozen,'' about convicts used as commandos.

Last week, Nelson was criticized by the department's internal watchdog, Michael Shaheen, for uninformative replies to inquiries about what discipline he imposed in some corruption cases in his agency.

Some officials fear that Nelson has a long-shot chance of succeeding Jensen, who many expect to move up to Deputy Attorney General.

''Meese is very personable and could well succeed here,'' said one career official who was impressed by the new attorney general's meeting with deputy assistant attorneys general on Wednesday. ''But he has to have the smarts not to name people like Alan Nelson or Bruce Fein.''

During the first term, Fein played a key role in framing the department's argument in the Bob Jones University case that private schools which discriminate on the basis of race are entitled to federal tax exemptions. That view was rejected 8-1 by the Supreme Court.

Now a legal analyst at the American Enterprise Institute, a private conservative think tank, Fein has been predicting that Meese will play a far more public role than Smith in articulating Reagan's policies, especially in ''the more contentious areas: racial and gender quotas, aid to religious activity, school prayer and abortion.''

The future of Assistant Attorney General William Bradford Reynolds, who as civil rights chief has stirred considerable opposition among black, women's and handicapped groups, also spawns concern in the department.

Reynolds has been helping Jensen brief Meese, and many think he will succeed Rex Lee as solicitor general, become deputy attorney general or succeed Jensen as associate if Jensen is promoted.

''I'd have real trouble with Reynolds as deputy or associate,'' said a presidential appointee who heads a Justice Department agency.

T. Kenneth Cribb Jr., one of the first Meese aides brought over from the White House, jarred administrative sensibilities by suggesting in a telephone call that the career secretaries in the attorney general's outer office be replaced.

In reply, Justice officials suggested the veteran secretaries possess invaluable, virtually irreplacable skills at getting a large bureaucracy to respond to an attorney general.

They stayed. In a reassuring act upon his arrival, Meese personally assured each one he wanted her to remain.

One of the department's most respected career attorneys, nine-year veteran Larry Simms, resigned as deputy assistant attorney general in the Office of Legal Counsel to join Smith's law firm. He was concerned about the ethical allegations raised against Meese during Senate confirmation hearings, associates said.

In separate meetings with the attorney general's staff, the heads of divisions and the deputy assistant attorneys general, Meese said he was impressed with the work of the department.

''He said there wasn't going to be a wholesale change, because Bill Smith built a good team and he wanted to build on that,'' said one official who was present.

''He came through and shook hands individually with everyone, had coffee for us, and said he wanted to hear our views and would be coming around to meet our people,'' said one of the deputy assistant attorneys general.

Meese told everyone that the rules which limit White House officials from contacting or pressuring Justice officials would remain in place. He broke up the attorney general's staff by joking, ''I know those people; you've got to watch out for them.''

--- EDITOR'S NOTE - Associated Press reporter Michael J. Sniffen has covered the Justice Department for more than five years.