Washington — It was a tough moment to face a crowd of reporters. Peter Hart, chief pollster for Walter Mondale, had just seen the latest newspaper survey, showing his man had fallen 22 points behind President Reagan.
''The Mondale campaign really feels very good,'' Mr. Hart observed wryly. ''We have avoided the one major pitfall that we saw facing the campaign - peaking too soon.''
Such self-deprecating humor runs through the Mondale staff these days. They are struggling to keep their spirits up, despite a shaky campaign beginning that makes some of Washington's most experienced Democratic veterans shake their heads in disbelief.
Even a staunch Democrat and Mondale supporter like Robert Strauss says that if the former vice-president doesn't rally his party soon, the results in November could be an ''electoral landslide'' for the President.
Somehow, says Mr. Strauss, Democrats must find a way quickly to put a ''positive spin'' on the news about the campaign. Otherwise, the race will be all over.
Political analysts outside the campaign agree that Reagan currently looks like a winner. But some of them are inclined to be less harsh on Mondale & Co. than even some Democrats are.
Richard Scammon, editor of the 14-volume ''America Votes'' series (1956-81), suggests that Mr. Mondale is running against both Mr. Reagan and the tide of history. That historical tide is definitely against the Democrats, at least in presidential races. It helps explain Reagan's huge lead.
A number of Mondale aides argue that if the campaign could be turned away from personalities and toward issues, the race would shift in favor of the Democrats. But Dr. Scammon disputes that. He says there is something stronger at work in this race than Reagan's winning personality.
''The problem always in this situation (is), when a guy is running behind, everybody assumes he is doing something wrong. . . ,'' explains Scammon. ''I doubt that (Mondale) is doing anything wrong.''
The Democratic ticket's real problem, he says, is history.
''If you take all the presidential elections since World War II, all nine of them, the Democrats have done well in only one, and that was in 1964. As a matter of fact, in only one other of those nine elections have they picked up more than half the votes - in 1976 when Jimmy Carter won by 50.5 percent.
Says Scammon: ''The Democratic Party does not have a natural majority in voting for president. . . . Mondale is caught up by history, and the history is that unless you get a disastrous scenario - as the Republicans did in '64 and the Democrats did in '72 - either the elections are extremely close, or there is probably a natural Republican majority.''
The natural Republican majority, adds Scammon, appears to be only for the White House. In the House of Representatives, the natural majority is with the Democrats, who have been in charge there since the 1950s.
Scammon doesn't try to explain the historical forces that have brought all this about. What has been overlooked, however, is that those forces for the first time in 12 years have once again put ''Northern liberals'' at the top of the Democratic ticket. The last time that happened, he observes, was when George McGovern was the party's nominee.
Democrats hope this won't be another '72 debacle. Mondale campaign manager Robert Beckel and Democratic chairman Charles Manatt each insist that because of early problems, the press and the pundits are writing off their candidate far too soon. They concede there have been glitches; but they point to several factors that could tighten the race by October:
* Volatility. During the primary campaigns, millions of voters waited until the final week or two before deciding on a candidate. New Hampshire saw a swing of 25 points in one week. A sharp turn toward Mondale is still possible, Mr. Beckel says.
* Geraldine A. Ferraro. The Democrats' vice-presidential nominee has been sidetracked for weeks - first by her financial problems, then by arguments with a Roman Catholic archbishop over the abortion issue. Now the House Ethics Committee has voted 12 to 0 to investigate whether she improperly refused to disclose her husband's assets on congressional reports.
Mondale aides need to find a way to get her back on the political offensive. They note that before her problems began, she had helped Mondale pull even with Reagan in the polls.
* Issues. Reagan's bedrock support is measured at about 35 percent of all voters. Nothing will move them. But other Reagan supporters are considered ''soft'' and wavering. Mondale is encouraged that an estimated 55 to 60 percent of all voters, including some counted for Reagan, disagree with the President on issues such as the environment, fairness, women's rights, and abortion.
* Leadership. Mondale wants to show himself tough on issues like taxes. He wants to depict Reagan as ''ducking and running.'' Mondale's tax plan - promising to boost levies on wage earners above $25,000 - is considered absolute folly by some party veterans, such as Horace Busby, a veteran of the Johnson campaign. But Mondale staffers say it was a risk they needed to take to portray him as fearless.
* Debates. Mondale desperately needs the debates. Democrat Manatt and Republican Lyn Nofziger, a Reagan adviser, each say that it now appears there will be two presidential debates. Mr. Manatt says the first will probably be around Sept. 30, the second in mid-October.
* TV ads. Democratic Party leaders unveiled their national television campaign this week. Insiders say the ads will probably get tougher and more anti-Reagan in the next three or four weeks.