In the strange world of political fund raising, liberal and conservative groups are gearing up for a boom year at the mailbox and the bank. Both -- for entirely different reasons -- think that President Reagan and the conservatives elected with him will be good for business.

The election gave liberals something that they badly needed to raise money: a crisis and an easily perceived evil to rail against in the form of Reagan and the New Right. Donations to civil rights, women's and environmental groups suddenly surged. Their constituencies feel threatened.

In the fund-raising business, it is always easier to raise money when a demon can be identified, according to direct mail experts.

"People don't give money in church to go to heaven; they give to stay out of hell," says one fund-raiser for liberal groups.

"Most money is given out of fear and anger," says another.

The election gave conservatives, long lonely voices in the wilderness, something they needed just as badly: victories to claim and a realistic prospect that their causes ultimately could triumph over the dastardly liberals.

Thus, the tom-tom beats coming out of the liberal and conservative camps this winter carry entirely different messages. Take these examples from the liberal community:

From Rep. Morris Udal (D-Ariz.), in a letter for Independent Action, a new political action committee: "Unless we start paying attention right now, a rightwing onslaught can take over the House of Representatives in 1982! Yes, unless we start to act now, we can face an unparalleled tragedy next year -- the total control of our Congress by forces determined to turn back the clock on all we have won in the past 20 years."

From former senator George McGovern, in a letter for the American Civil Liberties Union: "Not since McCarthyism in the 1950s has such a movement [the New Right] been so vocal, so well organized and so well financed. So zealous. . . . The danger is clear.The danger is present. The time to act is now."

From the Sierra Club: "The onslaught against conservation and environmentalism will begin in earnest in early 1981. Please heed this alert: eEnvironmentalists will face their toughest challenge in more than a decade. . . . We must meet the Reagan administration's anti-environmental juggernaut and stop it in its tracks."

The election caused an abrupt turnaround in memberships and donations to liberal women's, environmental and civil rights groups. The American Civil Liberties Union raised $500,000 in December 1980 -- $200,000 more than the previous December. Contributions to Common Cause, the self-described citizens' lobby, and the National Association for the Advancement 33 percent in December and November.

The National Organization for Women (NOW) picked up 12,000 new members in the same period; the National Abortion Rights Action League, a pro-abortion group, added 10,000 new members. Donations to the handgun control lobby skyrocketed 150 percent, due largely to the assasination of John Lennon. Environmentalists, hard pressed in their fundraising efforts during the last years of the Carter administration, suddenly found themselves a hot property again.

"Reagan is good for business," explains Roger Craver, of Craver, Mathews, Smith & Co., direct-mail firm that raised $50 million for 30 liberal groups and candidates last year. "People give money in times of adversity more than in times of tranquility."

Normally, Craver's firm would expect a drop-off in business of about $10 million the year after a presidential election. But this year the firm projects no such decline.

Conservatives, too, are looking toward a banner year. Richard Viguerie, the New Right mail expert, plans to double the size of his 275-member firm within the next 15 months, and start five or six new newsletters and a book club.

Viguerie concedes he was worried that Reagan's election would hurt his multimillion-dollar business, but claims his fears proved unfounded.

"Everyone's [conservatives'] mailings have gone through the roof since November. Our mailings at the Viguerie Company are doing better than ever before," he says. "Conservatives, in our lifetime, have never had any victories before, and they are excited and enthusiastic."

Conservatives are approaching Reagan from a direction that is opposite to that of the liberals.

"Ronald Reagan needs us; that will be our standard line," says Robert Heckman, chairman of the Fund for a Conservative Majority, which raised $3 million last year. "Ronald Reagan has a natural political home, and it is with us. Before 1980 Reagan was a national figure, not because he as a Republican or a former governor of California, but because he was the titular head of the conservative movement."

Conservatives are not going to let Reagan forget this. Many are taking a "let's keep Reagan honest" approach.The best example is the next issue of Conservative Digest, now in preparation at Viguerie's headquarters in Arlington.

Half of the issue, titled, "An Open Letter to Ronald Reagan," is devoted to "what has gone wrong with the Reagan transition," Viguerie says. "We name the good guys and the bad guys, and call for the firing of Pen James" -- Reagan's personnel chief.

A host of other groups have raised the same question. Their biggest complaint is that too few Reagan appointees are true-blue conservatives.

"By our reckoning, a mob of Nixon-Ford types are back in power, and a dismaying lot of them are neither [Reagan] loyalists nor anti-abortion," complained a recent issue a Lifeletter, an anti-abortion newsletter.

Strangely, many liberal groups are treating the new president much more gingerly than their conservative counterparts. A review of a dozen recent fund-raising letters from civil rights, women's and environmental groups finds that few attack Reagan directly and none mention the budget cuts his administration threatens to scores of programs long dear to liberals.

Instead, they focus their attention on the New Right, Moral Majority, The "right to life," movement, a few senators and administration appointees, the resurgence of the Ku Klux Klan, and the nation''s conservative political climate. Sens. Jesse Helms (R-N.C.), Strom Thurmond (R-s.c.) and Orrin Hatch (R-Utah), Interior Secretary James G. Watt, and television evangelist Jerry Falwell are favorite objects of attack.

Liberal fund-raising strategy recognizes the political popularity of budget cuts, and also deems it unwise to attack a new president.

Conservatives, on the other hand, feel compelled to put some distance between themselves and the president to justify donations to them.Meanwhile, they call for the appointment of more people like Watt and the election of more people like Helms. Thurmond and Hatch.

It all forecasts a classic ideological conflict, and one that conservatives enter with momentum and technology on their side. Out of power so long, conservatives have developed a far more sophisticated, broadly based fund-raising apparatus than liberals.

"There's going to be a big battle out there, and i'd bet on us," says Vaguerie.