On the night he launched his dark-horse bid for the presidency, Reubin Askew issued a warning to fellow Democratic hopefuls: "Get up early and stay up late because Old Rube is a-comin'."

Few are likely to notice very soon.

Askew, a two-term former Florida governor and a former U.S. trade representative, plans to run a lean, Lone Ranger campaign for the presidency, side-stepping many of the events and constituency groups that attract other candidates.

"I can't pull away from the pack if I run with them," he said in an interview. "I have to build my own constituency in the Democratic Party."

Askew, who held only one news conference during the 15-month exploratory phase of his campaign, plans to continue spending much of his time campaigning almost one-on-one with small groups of voters, leaving the crowds and the "candidate cattle shows" to better-known rivals, except when such encounters fit into his schedule.

"If I have to respond to every event, I can't have my own schedule and do the things I have to do," he said.

When the AFL-CIO met a few miles from his home in Miami recently, for example, Askew could not find a spot in his schedule to powwow with labor leaders. When Massachusetts Democrats held a fund-raising dinner, six presidential hopefuls showed up, but Askew was in Fort Lauderdale at a fund-raiser of his own.

He begins the campaign the darkest of dark horses, barely a blip on public opinion charts. His strategy is a classic underdog model, styled after those of George McGovern in 1972 and Jimmy Carter in 1976.

He intends to campaign early and everywhere, seeking delegates in all 50 states as a middle-of-the-roader unwilling to sell his soul to special-interest groups. He hopes to separate himself from the pack by being different.

"I'm willing to stick my neck out," he said. "I'm going to risk losing votes to try to get to the White House the right way."

Askew differs from the other Democratic hopefuls on several issues. He opposes legalized abortion, domestic content legislation and the nuclear freeze. His campaign will have its headquarters in Miami, not in Washington with his rivals.

Askew visited every state at least once last year, and Iowa and New Hampshire five times each. He has hired Dick Bouley, a longtime aide to the late governor Hugh Gallen, to direct his New Hampshire campaign. Marina Mennes, a former state party staff member, is heading his Iowa effort.

The Iowa caucuses and New Hampshire primary, the first two events of the presidential season, are critical to Askew. Aides said he does not have to win either state, just do better than expected, which at this point is not very well.

Both are relatively small states, the ideal setting for the type of personal campaign Carter waged in 1976 and Askew hopes to duplicate.

Askew also hopes the election-year calendar will work to his advantage. After Iowa and New Hampshire come 16 contests in one week. Seven are in the South, including the Florida primary with 143 delegates at stake.

As a moderate southerner, Askew hopes to do well in the region, although there could be two other southern Democratic candidates, Sens. Dale Bumpers (Ark.) and Ernest F. Hollings (S.C.). Former vice president Walter F. Mondale and Sen. John Glenn (Ohio) also plan major efforts in the region.

Florida is the only state where Askew has substantial support. Gov. Robert Graham, Sen. Lawton Chiles and many other Democratic leaders are backing him, at least for now.

The state is also a rich financial base for Askew. Since Feb. 23, when he announced his candidacy, he has raised $350,000 in Florida. This is enough to get him started, but Askew realizes that his home-state support could rapidly evaporate unless he shows strength elsewhere.

His campaign has not made much of a mark in Iowa, according to political observers there, But in New Hampshire, Republican Gov. John H. Sununu said Askew is "the one candidate who'll do better than you expect."

"Askew is much further along than Carter was in '75 in terms of contacts, fund-raising and acceptance by the party establishment," said Phil Wise, a former Carter White House and campaign aide now advising Askew. "In terms of putting together a tactical and logistics team, he's also further ahead. But I expect everyone else is, too."

Carter is Askew's inspiration and albatross, a ghost that haunts his campaign the way the ghost of Edmund S. Muskie, the 1972 front-runner, haunts current front-runner Walter F. Mondale.

On the surface, Askew and Carter have striking similarities. Both are moderate Democrats and born-again Christians--Carter a Baptist and Askew a Presbyterian--who served as governors of adjoining states during the same period.

Comparisons between the two men are inevitable. So are the brutal questions:

Is the country ready for another former southern governor as president? Or did Carter ruin it for everyone?

"I told him, 'You can't worry about that. You can't sit there and wring your hands all day about Jimmy Carter,' " one Askew adviser said. " 'If you do, you probably aren't ready to be a candidate.' Reubin Askew has to be his own candidate and his own man."

The candidate handles the matter gingerly:

"I'm not defensive about having worked for Jimmy Carter as U.S. trade representative , but I'm not Jimmy Carter. In all due modesty, I think I can be a better president than Jimmy Carter because Jimmy Carter gave me the opportunity to have the federal experience that he never had, nor did President Reagan."

Askew's campaign staff is small, and he plans to keep it that way most of the year. There are only 12 on his payroll, compared to Sen. Gary Hart (Colo.) with 18, Glenn with 40 and Mondale with 51.

Askew's staff is also inexperienced in national campaigns. Campaign manager James Krog was a top aide to Askew when he was governor and trade representative. Press secretary James Bacchus is a lawyer in Askew's Miami law firm who also worked in the governor's office.

His pollster is Bill Hamilton, and Orlando attorney Richard Swann, a leading Carter fund-raiser, is one of Askew's top money raisers. Former Democratic National Committee chairman Robert S. Strauss, Carter's 1980 campaign manager, has advised Askew on strategy and attended Askew's announcement news conference but has not endorsed him.

Askew's major asset may be time. Among the Democratic hopefuls, only he and Mondale are not officeholders and can campaign full time without having to rush back to Washington for key congressional votes.

That may not sound like much. But Carter and Reagan did not have jobs the year before their elections, either.