Though politics always plays a big part in filling Cabinet posts, President Bush has gone too far with his latest appointment.

His selection Friday of outgoing Rep. Lynn Martin of Illinois to become the next secretary of labor seems to betray either too high an opinion of Martin or too low an opinion of this particular job.Aside from political considerations, Martin's qualifications for the labor post are hard to discern. After teaching high school economics, government and English, she entered local politics and eventually graduated to the U.S. House of Representatives, where she served on the Rules Committee and the Legislative Process Subcommittee.

More discernible are her political qualifications. Among them are her longstanding ties to Bush, whom she backed in his first presidential bid in 1980 and served as national co-chairman of his 1988 presidential campaign.

Bush's political debts to Martin became deeper when the White House urged her to try to unseat Sen. Paul Simon last fall and she was defeated. But is this appointment really the appropriate way to pay those debts, particularly in view of Martin's lack of close ties to organized labor?

What a contrast, on all counts, to the selection of the previous Secretary of Labor, Elizabeth Dole. Dole was easily among the most capable and astute public servants in Washington. Before becoming secretary of labor in 1988, she served as secretary of transportation, where she pushed for mandatory seat belt laws, tighter security screening at airports and more sophisticated anti-collision devices for airliners. Before heading the Department of Transportation, Mrs. Dole served as a member of the Federal Trade Commission, a director of public liaison in the White House and executive director of the Commission on Consumer Interests.

Consequently, when Dole was tapped to head the Labor Department, it sent a signal that the White House was trying to repair its wounded relations with organized labor. The selection of Martin sends an altogether different message.

Viewed in proper perspective, the secretary of labor post is a big job that ought to be filled on the basis of more than just partisan rewards for partisan service.

The department, after all, administers federal laws on child labor, minimum wages, overtime and public contracts. It develops standards and policies for promoting the welfare of workers. It carries out federal laws on workers' compensation programs and handles appeals from federal workers regarding compensation. It develops apprenticeship standards for the training of skilled workers, administers laws dealing with the election of labor union officers and with union financial reports. It also regulates private pension and welfare plans.

The Labor Department also serves as the government's chief fact-finding agency in labor economics. It collect, analyzes, and publishes information on jobs and unemployment, industrial relations, occupation safety and health, price trends, productivity and technology, wages, family budgets, and economic trends. It protects the health and safety of workers by enforcing standards it develops.

Though the job of secretary of labor does not require technical expertise, it is still a big responsibility that requires firm, perceptive leadership. Part of that perception should be the realization that the Department of Labor is supposed to serve the best interest of all workers, not just the shrinking minority that belong to unions.

Maybe Martin is up to the challenge. Maybe. But it certainly is not obvious at this point.