A key man at the Labor Department these days is not a department official, nor even a government official.

He is Tennessee businessman and Republican activist William N. Morris, who is camped out at the agency as a one-man scouting party for Secretary-designate William E. Brock.

Morris, a longtime friend and aide to Brock, is interviewing top department officials to prepare Brock for his Senate confirmation hearings this month and to prep him for the key decisions he faces after confirmation.

But the unspoken part of Morris' agenda is to advise Brock on which, if any, of the 18 top political appointees left over from Raymond J. Donovan's four-year tenure should get the ax.

"There is high anxiety," said a high-ranking official. "Brock's people are very professional and are treating us very courteously . . . . But even though this is still the same [political] party and the same administration, we are going to end up job-hunting. The Brock people say that everything is status quo for the time being, but the operative words are 'time being.' "

However, another top staffer said the betting is that Brock will use "a scalpel rather than a meat-cleaver approach" when he makes personnel changes.

Among the first possible casualties, according to department sources, may be Robert A. Rowland, head of the Occupational Safety and Health Administration, and Francis X. Lilly, the department's solicitor.

Rowland, a Texas lawyer who was a key Reagan-Bush campaign official, has been strongly criticized by organized labor for OSHA's failure to develop new standards to control work-place hazards, particularly dangerous chemicals.

Sources said Brock is expected to replace Lilly because Brock will want his own person to serve as Labor's top lawyer.

Brock, currently U.S. Trade Representative, also is expected to bring with him his chief of staff, Dennis E. Whitfield, and his press spokesman, David Demarest, both of whom are former Republican National Committee officials.

Brock hasn't visited the department as the secretary-designate, nor has Donovan appeared there since he resigned to fight his indictment on fraud charges. Donovan, however, has called or written to thank his top staffers for their service.

Morris said in an interview that he will spend about two weeks, "as a favor to Bill," looking around the department and preparing a briefing book. Morris, 54, a former assistant Commerce Department secretary for trade development, is a corporate officer of three firms, including a coal company and a trading firm in Nashville and a Washington lobbying firm, Global USA.

"I've been very impressed with the people here," Morris said, "They are anxious for strong leadership and direction from their secretary. They want to do a job . . . and they will be excited because Bill Brock will give them the opportunity to get things done."

Brock paid a courtesy call last week to AFL-CIO president Lane Kirkland, a vocal critic of Donovan who welcomed Brock's appointment. AFL-CIO officials would not discuss details of their conversations, but a top Kirkland aide said, "I've already had more contact with the Labor Department in 36 hours than I did in the last four years."

Morris said he expects Brock to focus on the problems of youth employment and female workers. He said Brock "very strongly" supports the Youth Employment Opportunity Wage Act, which would cut the minimum wage to $2.50 for youths up to age 19 from May 1 to Sept. 30 as an attempt to increase summer job opportunities for teen-agers.

The department's Women's Bureau, criticized by Democrats for not playing a stronger advocacy role, will "focus more on outreach" to female workers, Morris said. JTPA UPDATE . . .

Training programs under the Job Training Partnership Act achieved a 68 percent job-placement rate among trainees between July 1 and Sept. 30, 1984, according to Frank C. Casillas, assistant secretary for employment and training, who termed the rate "fantastic" because it exceeded the department's 55 percent goal.

Starting wages under JTPA averaged $4.67. Nearly half the participants were minorities and 40 percent had been receiving public assistance prior to training, he said. CLOSING OFFICES . . .

The department is planning to close 10 field offices of the Office of Pension and Welfare Benefit Programs, a move that the department says will save money and increase efficiency. But some officials fear that it will "cripple" some investigations of pension- and health-benefit fraud because they will have to be conducted from distant offices.

Cities where offices would be closed are Pittsburgh; Cleveland; Minneapolis; Denver; Buffalo; New Orleans; Nashville; East Orange, N.J. -- and Honolulu and Puerto Rico (both of which have one-person offices).

About 70 investigators, auditors and support staff would be transferred to other offices.

These closings are in addition to plans to downgrade three of the department's regional offices -- in Boston, Seattle and Kansas City -- into area offices.