The Democratic Party heads toward the fall election believing that the electorate is once again ripe for its issues and its faithful are coming home.

But it is troubled that it may lack both the ideas and the money to fully redeem at the polls the opportunities created by the Reagan administration's economic failures.

As they wrapped up their midterm conference here, in which the overriding theme was party unity, Democratic leaders were predicting moderate rather than sweeping gains in congressional and state elections.

Most forecasts were for the party to hold its own in the Senate and pick up 15 to 20 House seats--figures that are in line with the historic norms for opposition parties in the first midterm election of a new administration.

Because of an unusual number of Republican governors who are either up for reelection or who have chosen not to run for reelection, the Democrats are expecting to pick up as many as a half-dozen governorships.

"The biggest problem we face out there . . . is they're going to try to buy the election," said House Speaker Thomas P. (Tip) O'Neill Jr. (Mass.), echoing a refrain heard repeatedly here the last three days.

The Republican Party has built up an awesome war chest for the fall. It is prepared to spend $11 million in House races, $10 million in Senate races, $10 million on a national advertising campaign, and millions more on support services. Democrats have only $1 million for House races, $1.2 million for Senate races and no money for advertising.

This has placed a tremendous burden on the party's candidates. And much of the political talk here was of money, not issues.

"I need $3 million. That's the reason I'm here," said Richard Celeste, the Democratic nominee for governor in Ohio. "I'm looking for people with money written all over them."

In dozens of Senate and congressional races, Democrats say that even after vigorous fund-raising efforts they expect to be outspent 2 to 1.

Jeff Bingaman, running against Sen. Harrison H. Schmitt (R-N.M.), said, "If I can only raise half as much as he does, I can win. If it gets worse than that, it's impossible. And I'm running in a traditionally Democratic state where we have a 2-to-1 registration edge."

There is, of course, a large dose of political posturing in the Democratic complaints over money, with the party clearly trying to exploit a they're-buying-your-vote theme to maximum partisan advantage.

Traditionally, individual Democratic candidates have raised more for their campaigns than Republicans, and they get more in-kind help from unions and other interest groups. So the money deficit, though daunting when Democrats consider only national party fund-raising, is moderated by other nuts-and-bolts considerations.

The other thing that had some leaders worried here this weekend is that their party, after it gets through lambasting "Reaganomics," still hasn't figured out what coherent, cohesive message to deliver next.

Should it take the opening created by the ills of a Republican economy to revive the old-time religion of a big, activist, compassionate government? In theory, anyway, Democrats still like to think of themselves that way; this weekend demonstrated anew how those appeals remain the most sure-fire applause lines in any Democratic convention hall.

Or should it take on some of the complex new economic realities of the 1980s, fashioning programs to deal with high interest rates and diminishing capital investment and with an economy that is shifting from a manufacturing to a service base.

There is a tension, very much unresolved, between the traditional Democratic people-helpers and the neo-liberal Democratic economy-fixers, or, as they are sometimes called, the "Atari Democrats," who talk about investing in exotic things like high technology and "human capital."

The best to be said about the workshops this weekend is that they were the beginning of a dialogue on these matters. But others take a dimmer view. "These neo-liberals are a diversion that help keep Democrats in disarray," said Rep. Tom Harkin (Iowa). "They're trying to tinker and fine-tune, and you're not going to capture the spirit of the Democratic Party with tinkering."

Ideological warfare is nothing new to Democrats, of course, and the scraps of today pale in comparison to the internal bloodletting of the Vietnam era. For that, the party is happy. For the failures of Reaganomics, it is ecstatic.

Unemployment, high interest rates and federal budget cuts have hit all the traditional parts of the Democratic constituency particularly hard. They have united women, blacks, liberals, environmentalists and organized labor against a common enemy: Ronald Reagan.

Pollster Peter Hart says that four months before the election these groups are "locked in" to Democratic candidates. "They have come home to the party," he says. "They've already made up their mind who they will vote for."

The irony of the Democrats' current fortunes is not lost on party leaders.

"Let's not kid ourselves," Rep. Gillis W. Long (La.) said today. "The opportunity we have comes not because of what we have done, but because of Republican failures."

Hart and other Democratic pollsters have told Democratic leaders that 1982 will be "a big issue election," focusing largely on the nation's economy.

"The agenda is set for '82," he says. "The psychology is already here."

Democrats see their advantage clearly. "There's nothing wrong with trickle-down economics, but when was the last time anyone you know was trickled down on?" asks Sen. Wendell H. Ford (Ky.), chairman of the party's Senate campaign committee.