A bunch of Ronald Reagan's admirers want to raise about $50 million to help him in the fall. You'd think he'd be ecstatic.

But Reagan and his closest advisers aren't. In fact, the prospect of all those millions flying about has the advisers worried half silly.

"Ordinarily, you welcome all the help you can get," says Nevada Sen. Paul Laxalt, Reagan's campaign chairman. "But here you have that fear that you'll have some unguided missiles flying around out there . . . You just hope it doesn't backfire in your face."

What bothers Laxalt and others in the Reagan inner circle is they won't be able to control how the money is spent, or even talk with the people who raise it. They fear the fund-raising groups will do something to embarrass the campaign, and give Jimmy Carter ammunition to charge that Reagan is trying to buy the election.

"They are a complete wild card. We can't control them," said a key Reagan adviser. "We don't know what they're going to do. I hope they don't get in the way of what we're doing."

The Democrats are already trying to make political hay out of the fund-raising efforts. They charge that Reagan forces are trying to subvert federal campaign-spending limits by a legal loophole.

Common Cause, which led the fight for election-law reform in the wake of the Watergate scandals, has proven a ready ally. It plans to file suit this week to stop the pro-Reagan groups. The groups, Common Cause president Archibald Cox said last week, "threaten a return to the old Watergate tactics and influence of money in elections."

Under current law, the nominees of both major political parties will receive $29.4 million each in public funds to conduct their campaigns. That is all they are supposed to spend. But a 1976 Supreme Court ruling provides that individuals or committees can spend unlimited amounts for or against candidates as long as they act independently of the campaigns.

So far, five "independent expenditure" groups are working to raise money for Reagan. If they meet their fund-raising goals (which is very much in doubt), they could double or even triple the amount of money available to Reagan, the expected GOP nominee.

(One anti-Reagan group, "Americans Against Reagan," is being formed in California.)

What worries Reagan strategists is that one or more of the groups may go off halfcocked. Anticipating that President Carter will wage a vicious anti-Reagan campaign, they fear some groups will overreact and issue negative ads and statements that will give the entire Reagan effort a Nixonian flavor.

Ironically, one of the reasons several of the groups formed was serious misgivings about the ability of Reagan's own organization to conduct a winning campaign.

"I don't know why the Reagan campaign is worried about us. They better start being apprehensive about their own campaign," says Terry Dolin of the National Conservative Political Action Committee, which has formed a Ronald Reagan Victory Fund. "I don't think they've ever gotten control of their own campaign. They don't have anyone in charge. I've never seen so many dumb things come out of one campaign as have come out of one campaign as have come out of the Reagan campaign this last month."

Dolin's group, closely associated with what's called "The New Right," hopes to spend from $500,000 to $2 million. It plans to unveil the first "independent expenditures" Reagan television ads within the next week.

In one ad, pictures of former Carter aides flash across the screen as an announcer says:

"In 1976, Jimmy Carter said, 'Why not the best?' That's what he said. Now look what he gave us: Andy Young, the man who called Ayatollah Khomeini a saint, forced to resign after lying to the president; Bert Lance, forced to resign for questionable banking practices; Peter Bourne, forced to resign for supplying drugs to a White House staffer."

Another group, Citizens for Reagan in '80, an offshot of the Fund for a Conservative Majority, is thinking along the same lines. It wants to raise $3 million to $10 million, and has already taken in $908,000, more than half of which it spent in Reagan's behalf during the primary season.

Robert C. Heckman, chairman of the group, is reviewing a series of scripts that picture Reagan as surrounded "by men of distinction" and Carter as surrounded "by inept cronies from Georgia."

"We want to show Reagan as a man who managed a government for eight years in California and is up to the task of being president as contrasted to Jimmy Carter, who we call the Peter Principle president," said Heckman, who is also executive director of Young Americans for Freedom.

The other Reagan groups are:

Americans for Change, headed by Sen. Harrison Schmitt (R-N.M.), who has put together a prestigious steering committee including Sen. Dave Durenberger (R-Minn.), former defense secretary Melvin Laird, former Michigan governor George Romney and former Nebraska senator Carl Curtis. The group hopes to raise from $20 million to $30 million, much of it from wealthy donors able to give $1,000 or more.

A yet-unnamed group put together by Thomas Reed, a longtime Reagan supporter from California, and two Nixon administration officials, Peter Flannigan, a New York broker, and Rod Hills, a Washington attorney. Originally, Stuart Spencer, a political consultant who directed Gerald Ford's 1976 campaign against Carter, was slated to run this committee, but he has been dropped.

The committee has also halved its original goal of raising $12 million to $15 million. It hopes to launch a sophisticated media campaign put together by John Deardourff, a respected expert, and targeted at a half-dozen swing states such as Pennsylvania, Ohio and Michigan.

The group briefly considered joining forces with the Schmitt committee, bud decided against it. However, Reed has rented office space in Room 319 at 218 N. Lee St. in Alexandria, next door to Americans for Change, and they share a switchboard and Xerox machine. Both groups insist the location was purely concidental.

Americans for Reagan, an offshot of Sen. Jesse Helms' North Carolina-based Congressional Club, which hopes to spend about $500,000.

In an emotionally worded fund-raising letter, Helms says the money is needed to offset "some of the most powerful forces in the country which are working to destroy the Ronald Reagan candidacy. What are those forces? They are the liberal news media, union bosses, liberal and left wing politicians, institution leaders and organizations devoted to forcing socialistic programs and doctrines upon the American people.

"I fear very much that the awesome power of the liberal press and the broadcast kingmakers will once again succed in defeating the American people. But this time they must not succeed."