They are five good men and true. Only one of them -- Sen. Bob Dole of Kansas -- is known to the general public, and that, arguably, less because he once ran for the Republican presidential nomination than because he is half of a publicized wife-and-husband political team with Transportation Secretary Elizabeth Dole.

The other four could pass through an airport almost anywhere without causing heads to turn: Sens. Ted Stevens of Alaska, James McClure of Idaho, Richard Lugar of Indiana and Pete Domenici of New Mexico.

They have the kind of earnest but unremarkable faces one associates with middle-aged Republicans. The youngest is 52; the oldest, 61. All but Lugar are lawyers. All are professional politicians and lifelong Republican loyalists. Last year they voted with President Reagan eight or nine times out of every 10 roll calls testing the president's policies.

The five men are rivals in the election on Wednesday to choose a successor to retiring Senate Majority Leader Howard H. Baker Jr. of Tennessee. It is a contest that has excited a great deal of curiosity and speculation in Washington since Election Day. But given the surface similarities of the five men, you have to wonder why anyone other than the contestants and their supporters should care about the outcome of the secret-ballot voting.

The answer you get, from senators and from students of Congress, is that the position is one of the three or four most important in our government, and it may be particularly crucial during the next few years.

"The majority leader is the traffic cop," says Tom Korologos, who lobbied for the White House and now represents major private clients. "He decides which bills come up and which don't. His schedule determines the legislative priorities.

"But that is just the beginning. He also speaks for the Senate to the other parts of government -- to the White House and to the House of Representatives. He is the contact point with the opposition party. And his impact is not confined to legislation. He advises whether presidential appointments can be confirmed -- and takes on the responsibility of confirming them. And on foreign policy, a groan from the majority leader can really make waves."

Baker played all these roles in his four years as majority leader -- and played them so well that his shoes will be hard to fill. His contribution was especially noteworthy, since he was called upon to play counselor both to the newly elected president and to the biggest crop of freshman Republican senators -- 16 of them -- in ages.

As a veteran Senate staff member said, "It was the alliance between Ronald Reagan and Howard Baker that made it possible for Reagan to change the course of government."

But no one in the Senate conceives of the majority leader's role simply as an agent of the president. McClure, who was the earliest Reagan supporter among the five men seeking the post, made the point in an interview that "Howard Baker was an opponent of Reagan (in the 1980 primaries), and no one could have been more faithful than Baker in trying to get Reagan's program through."

Moreover, McClure said, "people in the Senate want a capable leader who can present the Senate view to the administration, and not be just a rubber stamp. . . . Sometimes the best thing you can do for the president is to describe accurately the limits on his options."

In 1985 those limits are likely to be severe. A net loss of two seats in the Nov. 6 election reduced the Republicans' margin in the Senate to a shaky 53-47 majority. A scary 22 of those Republican seats will be at stake in 1986, which means those senators will not have the luxury of the long-term viewpoint.

At the same time, as Sen.-elect Phil Gramm (R-Texas) pointed out last week, there are minimal prospects of Reagan's reviving the conservative coalition of Republicans and southern Democrats in the House that disappeared with the 1982 election. Gramm, who was a key architect of that coalition in 1981 before switching parties and running for the Senate, said: "There just aren't enough (conservative) people there" now to make it work.

His conclusion -- and that of most other observers -- is that the first test of credibility for any Reagan proposals will be their capacity to command the support of most Senate Republicans. But since those Republicans span the ideological spectrum, the majority leader -- whoever he is -- will probably need some Democratic votes to pass any controversial measure.

As Domenici, another of the leadership contenders, pointed out, the only way the Senate can act -- given its loose rules and tradition of tolerance for even obstructive minorities -- is by the majority leader's mustering the institution's will to act. "The leadership of the United States Senate will either cause some things to happen that the country needs," Domenici said, "or will prevent their happening. The performance will be directly measurable."

That is no exaggeration. Outsiders' judgments -- including the White House's -- will not affect the choice of a majority leader. But everyone, including the president, truly does have a great deal at stake in the identity and the success of Baker's successor.