Former Indiana governor Otis R. Bowen and Interior Undersecretary Ann Dore McLaughlin are the leading candidates to become secretary of health and human services, succeeding Margaret M. Heckler, informed White House officials said yesterday.

A third person on the list, although White House aides do not consider him a leading candidate, is former California Republican Party chairman Tirso del Junco, the officials said.

President Reagan is expected to decide on Heckler's successor shortly, officials said.

Heckler agreed last month, under pressure from White House chief of staff Donald T. Regan, to accept nomination by the president as ambassador to Ireland.

The White House has cast a wide net for a successor, one official said, including a search of state health officials and medical industry executives.

Regan has interviewed Bowen and McLaughlin, officials said.

Bowen, 67, Republican governor of Indiana from 1973 to 1981, is clinical professor of family medicine at the Indiana University School of Medicine. He has served on a number of federal advisory commissions, including one that recommended a major increase in federal alcohol and tobacco taxes to help shore up the Medicare hospital trust fund.

According to an Associated Press account, Bowen told an American Medical Association convention in 1981 that he gave the drug dimethyl sulfoxide (DMSO) to his dying wife to relieve her pain. DMSO is not approved for human use for pain relief.

Bowen said the drug was provided to him by a veterinarian friend, and he criticized the Food and Drug Administration for delays in approving drugs that ease pain for dying patients.

McLaughlin, 43, has been in the second-ranking post at the Interior Department since early last year and is responsible for much day-to-day management. She also has been used as a troubleshooter at the department, taking on sensitive problems for Secretary Donald Hodel.

McLaughlin, whose husband, John, hosts "The McLaughlin Group" news analysis program on television, is well-regarded by Regan and served as assistant secretary for public affairs when he was Treasury secretary. She was part of his inner circle that met daily to discuss press, legislative and other matters.

When Regan came to the White House, there was speculation that McLaughlin would become one of his senior advisers, perhaps White House communications director. But she decided to remain at the Interior Department, and had expressed interest in a Cabinet post.

McLaughlin was director of communications in 1971-72 for President Richard M. Nixon's reelection committee, assistant to the chairman and press secretary for the 1972-73 Presidential Inaugural Committee, director of the office of public affairs at the Environmental Protection Agency from 1972 to 1974, and a government relations and communications executive at Union Carbide Corp. before coming to the Reagan administration in 1981.

Del Junco, a Pasadena, Calif., surgeon, is a longtime Reagan backer who was credited with bringing record numbers of Hispanics to the GOP in the 1982 and 1984 elections. Born in Havana, he was a member of the Presidential Commission on Broadcasting in Cuba, and was recently appointed to serve on the University of California Board of Regents.