In the aftermath of President Reagan's landslide victory over Walter F. Mondale, a forgotten power group has reemerged in American politics: white men.

In a year when Jesse L. Jackson and Rep. Geraldine A. Ferraro (D-N.Y.) made political history, white men turned out to be the president's most significant supporters. Rather than the "year of the woman," as 1984 started, the reelection of Reagan may best be remembered as the "year of the white male."

At a time when the gender gap was on the lips of almost every political analyst, when experts warned the Republicans that Reagan's apparent unpopularity among women threatened his reelection, when the Democrats sought to recapture the White House by swelling the electorate with millions of new black, female, Hispanic and poor voters, Reagan's lock on white men turned demographic analysis on its head. The beast was so large that everyone ignored it.

Reagan won every category of white males except white Jewish males, according to exit polling by ABC News. He won rich and poor, Catholic and Protestant, young and old, North and South, "Yuppie" and blue collar. Generally he won them by overwhelming margins.

The president took 59 percent of the total vote Nov. 6, but 66 percent of white men, according to ABC exit polls. In the South the figure was 74 percent, in the West 68 percent.

Much was made of Mondale's majority among the poorest people in the country, but that was because of the votes of women and minority-group members. According to ABC News, Reagan got 54 percent of the votes of white males earning less than $5,000 and 57 percent of those earning $5,000 to $10,000. He also got 75 percent among those earning more than $50,000.

Exit polls also showed that Mondale carried voters in union households, but Reagan captured the white men in union households, by a margin of 54 percent to 46 percent, according to ABC.

Surveying the wreckage after the election, Democratic pollster William Hamilton said of Reagan's strength among white men, "We missed an entire group that constitutes the size of the electorate that Walter Mondale got."

Hamilton called it "a story of omission -- of us missing the boat on how to communicate to them." And he warned that the Democrats "can't very well lose the white male vote by 2 to 1 and expect to be serious players in a two-party system."

"Ronald Reagan communicates certain personality traits," said Robert Teeter, a Republican pollster. "Women say it's the macho thing. It's not. It's the degree of self-confidence and self-assuredness that comes across. That's the characteristic that makes him so appealing to men."

Teeter said he believes that white men responded to Reagan because the president made it clear he doesn't want the United States to get shoved around by other countries -- not by the Soviet Union and especially not by lesser powers.

At home, Reagan appeared unapologetic about criticism that he didn't do enough to help the poor. To some white men -- a group threatened by greater opportunities in the work force for minorities and women -- that, too, may have been part of Reagan's appeal.

That Reagan was especially in tune with white men is seen in the responses to a question asked in a Washington Post-ABC News poll taken in September: "Which one do you think cares about people like you, Reagan or Mondale?" Among all registered voters, Mondale was chosen 49 percent to 43 percent. White males, however, thought Reagan cared more about them, 51 percent to 40 percent.

White men saw Reagan as a leader. By 77 to 20, they thought Reagan had strong leadership qualities; by 53 to 43, they thought Mondale did not.

Asked if they were better off financially under Reagan -- a key indicator of how people voted -- 62 percent of white males said yes, compared with 53 percent of all registered voters.

Sixty-five percent of white men said they trusted Reagan more than Mondale to deal with the economy; 62 percent said they trusted him more than Mondale on foreign policy. In each case, that was roughly 10 percentage points higher than the overall national sample of registered voters.

Reagan's popularity among such a dominant demographic and economic group is certain to influence the debates over winners and losers as Congress and the administration decide how to reduce the federal budget deficit and promote economic growth.

Reagan's strength among white men also raises troubling questions for the Democratic Party as it seeks to dig out from last month's avalanche in the presidential race.

Reagan won 70 percent of the vote among white males aged 18 to 24 and 40 to 49. He won 67 percent of the vote among those aged 25 to 39.

He got 73 percent of Protestant white males, 62 percent of Catholic white males and 79 percent of those white males who call themselves "born again."

But among Jewish white males, Mondale captured 61 percent to Reagan's 39 percent.

Among self-identified white male Yuppies -- those young, urban professionals first drawn to Sen. Gary Hart (D-Colo.) in the Democratic primaries and the target of both parties as they look to the future -- Reagan got a whopping 74 percent.

Already this has affected Democrats, some of whom have begun to court white males as if they were another constituency group.

Lee Atwater, deputy director of the Reagan-Bush campaign, summed up the irony of the postelection landscape. "A year ago, all of us were very concerned about the gender gap," he said. "As it turned out, there was . . . a male gender gap for Mondale."