Last year, when Howard H. Baker Jr. (R-Tenn.) left elective office after three terms in the Senate, one abortive run for president and a childhood as a "congressional brat," he said he wanted to get a "civilian perspective."

Today, he finds himself battling the dirty little rumor that he's signed on for life.

The former Senate majority leader served as an unofficial host of the Southern Republican Leadership Conference here in his home state, and he used the occasion to deliver some pointed forget-me-nots about his continuing designs on the White House.

Baker announced that Tennessee Gov. Lamar Alexander (R) will chair, and former New Hampshire attorney general Tom Rath will direct, the Baker Committee, an exploratory group that will lay the groundwork for the 1988 GOP nomination contest.

He also said his reading of the early presidential sparring in his party has left him convinced that " Vice President George Bush doesn't have it locked up; there is a growing perception that no one has it locked up."

But there is also a growing perception, at least among the political junkies who puzzle over such matters year-round, that Baker's handsome reentry into civilian life -- where he earns in excess of $1 million annually from two law firms (Vinson & Elkins in Washington and Baker Worthington in Knoxville, Tenn.) and three corporate directorships (MCA, AT&T and Gannett) -- may have doused some the "fire in the belly" any candidate must have to run for president.

"It's the biggest problem we face; it's the thing we keep hearing over and over," said Rath, a former campaign strategist for Sen. Warren B. Rudman (R-N.H.).

"The good side of it is that all the Republican candidates have their own unique problems, and ours is the easiest to resolve. We get rid of it simply by running," Rath added.

To prepare for that day, Rath will spend roughly half his time this year managing the Baker Committee from his law office in Concord, N.H. He'll help Baker build a grass-roots base in that key early primary state, and he'll hire a staff of up to eight to gear up activity around the country. The committee expects to raise and spend in excess of $1 million this year.

Baker, 60, who said it "boggles my mind" that the nomination process is under way so early, has long advocated that presidential campaigns and legislative sessions alike be shortened. The early activity of his rivals has forced him to "accelerate the pace" of his preparations, he said.

He will not, however, mount a major campaign effort in Michigan, where the state GOP this summer will hold the first stage of its four-stage delegate-selection process. Rath said Baker may try to organize in selected areas of the state, to make a symbolic showing. By this fall, Rath said, Baker will be on the stump virtually full time, campaigning for Senate and House candidates around the country.

But even as Baker becomes more visible, skepticism about his candidacy remains. "It's hard to see where he fits," said David Keene, a veteran GOP campaign operative who is a political consultant to Senate Majority Leader Robert J. Dole (R-Kan.), another probable 1988 hopeful. "He's learned the wrong lessons of history. He saw that Jimmy Carter won in 1976 and Ronald Reagan in 1980 by being out of office, so he gave up his seat. But he's left himself with no forum."

Baker said he is not ready to begin articulating where he "fits," but his Senate record makes it clear that it will be on the moderate side. His vote in favor of the Panama Canal treaty and his general lack of interest in pushing the conservative social agenda has made him few friends on the right. Since leaving office, he has advocated a tax increase dedicated to deficit reduction, a position that will win him few supply-side supporters.

Baker's strategists have a battle plan for 1988. While other candidates scramble for the affections of the right, Baker's appeal to moderation and skillful management might allow him to make a breakthrough in New Hampshire. "We have to do well there, maybe even win it," said Baker spokesman David Spear. From there, Baker hopes to score heavily in the flurry of southern primaries that will follow within a week.

Baker likes the idea of a southern regional primary that is now percolating in statehouses throughout the South. "I'd be the only one in the race who can detect no accent on the part of the participants," he said.

In 1980, Baker's presidential bid never made it into the South; he dropped out after poor finishes in Iowa and New England.

In 1980, the rap on Baker was that he had too much the legislator's demeanor -- his personality was too rounded, his instincts too much toward conciliation -- to be appealing as a presidential candidate.

Now he's a civilian, not a legislator. The question is: Will it matter?