The White House began winnowing names yesterday for a successor to Commerce Secretary Malcolm Baldrige, who was killed Saturday in a freak rodeo accident, but it indicated that there was "no hurry" to replace the first Cabinet secretary to die in office in almost 40 years.

While the two prime candidates are already in the Commerce Department, a number of other well-known Republicans, both in and out of the administration, figured in informed speculation here. A senior administration official said that President Reagan would not focus on a successor until after a memorial service for Baldrige here Wednesday and his funeral in Connecticut on Thursday.

"We're not going to be able to find anybody that's going to fill Mac's shoes," Treasury Secretary James A. Baker III said in a tribute to Baldrige on the McNeil-Lehrer News Hour last night.

Reagan and Vice President Bush will deliver the eulogies at Wednesday's memorial service at the National Cathedral, which will be presided over by Sen. John C. Danforth (R-Mo.), an Episcopal minister.

In the meantime, one of the prime candidates -- Deputy Secretary Clarence Brown Jr., an Ohio congressman for 17 years who became number two man at Commerce after losing a race for governor in 1982 -- took over as acting secretary.

Brown, who has not played a major public role in the department's activities, said he talked briefly about succession yesterday with White House chief of staff Howard Baker.

Another major contender for the post, Commerce Undersecretary Bruce Smart, is favored by many business executives and some within the department because of his strong experience in enunciating administration trade policies, which will be one of the major tasks of the Commerce secretary in the 18 months remaining in the Reagan administration.

But Smart -- like Baldrige, a former corporate chief executive officer -- is not believed to have enough political clout in the White House to win the nomination. There were reports, moreover, that some administration officials felt it would be wrong to promote him over Brown, a longtime Republican loyalist.

Within hours of Baldrige's death on a northern California ranch, Brown had his aides summon key Commerce officials to a meeting, held early yesterday, that he opened with a prayer for Baldrige, department sources said.

Later he told Baldrige's personal staff, including long-time executive assistant Helen W. Robbins and special assistant Mitchell Stanley, that they should work full time planning the memorial service and helping Baldrige's widow, Margaret. Brown also ordered that all papers from the White House flow into his office instead of being routed through the secretary's office.

Among others named as possible replacements for Baldrige were U.S. Ambassador to France Joe Rogers, former Tennessee governor Lamar Alexander, and two present members of the Cabinet, U.S. Trade Representative Clayton Yeutter and Labor Secretary William E. Brock. Both Brock and Yeutter indicated through aides, however, that they had no interest in moving into the Commerce post.

"They need to come up with somebody who is easily confirmable," said an administration official of the White House search.

One of the most important tasks facing a new Commerce secretary is dealing with Congress on a trade bill, which is likely to emerge from a joint House-Senate conference early this fall. Secretary Baker, who played a lead role with Yeutter and Baldrige in working with Congress on trade legislation, called Baldrige "a very talented person who could help us substantially in working with Congress.

"He had a special relationship with those people up there" on Capitol Hill, Baker said, adding that his death means that "others of us are going to have to work harder," an indication that Brock -- a former U.S. trade representative, congressman and senator -- may increase his role in the trade debate even if he is not in the Commerce post.

Because of the prominence of the trade bill this fall and the policy debate with Congress and within the administration, business leaders speculated that it would not be hard for the administration to find someone to take the Cabinet post even though the job will end in 18 months.