President Reagan's reelection campaign is gathering steam on all fronts except one: the candidate.

A reelection committee will open its doors in six weeks. Across the country, state chairmen are being selected. Organization charts have been drawn for the campaign staff. A direct-mail appeal to 2 million Americans will be launched this fall, seeking money to support the Reagan reelection effort.

But by several accounts, Reagan is reluctant to become part of his own campaign until the last possible moment, even though preparations are moving ahead with his tacit approval.

This is partly a strategic decision based on the experience of previous presidents who saw their power slip away when they became official candidates too early. But it also appears to be a personal decision for Reagan. This is the last campaign of his political career, and he seems content to take his time getting started.

"He comes up to the starting blocks as a very reluctant runner," said one Reagan associate from previous campaigns. "He is not there yet. He has not made the decision absolutely firmly. But when the gun goes off, he will be in the starting blocks."

According to current plans, Reagan will not be in the "starting blocks" to make his official announcement speech until late November or early December, after his planned trip to the Far East, although aides stress that there is no direct link between the trip and Reagan's announcement. The president reportedly has said privately that he would prefer to wait until January to announce, although his staff would like it sooner. The only decision Reagan could make now that would surprise his staff and political associates would be to retire. A White House official said the only reason Reagan would bow out now would be because of "health or terrible polls," neither of which appears to be an obstacle today.

This summer, Reagan has been testing campaign themes and working key constituencies and states. He has been refining one-liners and building a rhetorical defense of his first term.

His August political swing through Florida, California and Texas served to highlight both the strengths and vulnerabilities of the Reagan reelection effort as it gets under way more formally in the weeks ahead.

For example, the Reagan entourage was caught by surprise when former Justice Department official Barbara Honegger charged that Reagan had made a "sham" of the program to eliminate gender discrimination in federal and state laws. Her complaint, coming just as the White House was seeking to improve Reagan's standing among women voters, served to focus more attention on one of his persistent political problems, the "gender gap," in which women give him lower approval ratings than men do.

Behind Reagan's campaigning among Hispanic voters this summer lies another political trouble spot: the expected high registration and turnout of black voters in 1984, which could prove particularly worrisome for Reagan in southern states. The Reagan strategy is to build support among Hispanics as a buffer to the expected black vote for the Democratic nominee.

Reagan also showed in his summer politicking that he intends to take full advantage of what his advisers sometimes call the "engine" of his reelection drive: economic recovery. In virtually every speech, he is playing recovery to the hilt as a vindication of his much-criticized economic policies and the biggest success of his first term.

And, just as he did in 1980, Reagan sought this summer to use self-deprecatory humor to answer questions about his age and health, hoping to blunt doubts about both before they become a larger issue.

It is also clear that Reagan intends to exploit another strength he brings to the 1984 campaign: He has no primary challengers. As a result, he can take a back seat when the Democrats are fighting for the nomination late this year and early next.

The conventional wisdom among Reagan's political advisers is that Sen. John Glenn (Ohio) would provide Reagan with the stiffest challenge among the Democratic contenders.

The organizational side of the Reagan reelection effort is well under way. The White House political affairs office is scheduled to close Oct. 15. Edward J. Rollins, political affairs director, and his deputy, Lee Atwater, will open the reelection committee soon thereafter. They will be assisted by two old hands from the early stage of the Reagan 1980 campaign, GOP political consultant Charles Black and press secretary James Lake.

Once the committee is formed, Reagan will have 15 days under federal election law to give it his blessing, which he is expected to do about Nov. 1. Officials said that while Reagan wants to wait until later for his announcement speech, the reelection committee could not be delayed because it must start the direct-mail fund-raising effort before the winter holidays.

Using contributor lists from the Senate and House Republican campaign committees, the Reagan campaign will send out about 2 million direct-mail appeals. These contributions, up to a maximum of $250, can be used to apply for matching federal funds. Reagan's advisers now envision a $30 million campaign budget for all of 1984, of which a maximum of $10.5 million will be federal funds.

The themes of the Reagan reelection effort are also emerging. He is portraying himself as a champion of economic recovery. One of his favorite campaign lines this summer has been to say that the Carter presidency was a time when "our leaders were throwing up their hands, talking of a national malaise . . . . "

"You know, inflation was supposed to be institutionalized, couldn't get rid of it in less than decades," Reagan told a GOP fund-raiser in California two weeks ago. "Well, we just didn't know that, so we did it." And, he added with emphasis, "You don't hear them calling it 'Reaganomics' anymore."

Other themes stress the revitalization of the military and Reagan's conviction that his approach of "peace through strength" will bring the Soviets to agree to nuclear arms reduction, a conviction he has yet to turn into reality. Reagan also is stressing, as he did in 1980, the traditional family values he claims to share with voters.

Reagan, 72, jokes about his age in ways that seem designed to deflect concern about it, a device that accomplished the same purpose four years ago. When a group of Republican women were shouting " '84! '84!" before he spoke to them in San Diego recently, Reagan shot back, "I don't mean to be critical, but 84, I'm not that old."

In a similar vein, when Reagan left an appointment with his doctor for a hearing examination in Los Angeles, reporters shouted, "How is your hearing?" He replied jokingly, "What?"

In terms of geographic strategy, the White House is approaching the campaign gingerly. The general approach, says one of Reagan's 1980 regional political directors, is to "build from your strengths" and, as the campaign goes on, attack the more difficult targets. Thus, Reagan's strategists begin with his "base" in the West. They generally believe he must win Texas and Florida as well as California, all states with large and potentially potent Hispanic populations.

The current assessment is that the South is far more fluid than it was in 1980 and much will depend on who the Democrats nominate. The anticipated heavy turnout of black voters in the South next year is of some concern to the Reagan camp. "If you look at the 1980 margins, it gives pause for concern," said one official.

In the Midwest, the Reagan strategists fear the loss of key industrial states such as Ohio, particularly if Glenn is the Democratic nominee. But they say they hope that a strong economic recovery in the smokestack industries might help Reagan in the final throes of the campaign.

Reagan also intends to take advantage of his incumbency. It was no accident that in back-to-back appearances with Glenn at the Veterans of Foreign Wars convention this summer, Reagan chose to sign a veterans job training bill, or that while in El Paso for a speech to Hispanics he announced some federal efforts to deal with economic problems along the U.S.-Mexico border.