Two years ago, shocked by President Reagan's supply-side steamroller, Democrats in Congress were beset with self doubt. Liberalism seemed to be a dirty word. Liberals became neo-liberals, southern Boll Weevils turned bipartisan--one became a Republican--and everyone went looking for new ideas.

Now, however, the Democrats are feisty and confident. With 26 new Democratic seats, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) should in fact control the House. A chastened Republican-controlled Senate, fearful for the 19 Republicans up for reelection in 1984, strengthens his hand.

"The Democrats feel resurgent," said Rep. George Miller (D-Calif.), chairman of the new Committee on Children, Youth and Families. "We're getting back to mainstream Democratic politics. People are remembering that government has a role to play."

Rep. Henry A. Waxman, Miller's California Democratic colleague, agreed.

"Two years ago the Republicans were called the party of fresh, new ideas," he said. "We tried their ideas and got into a lot of trouble. We're not going to try any more gimmicky theories."

This week, as the uneasy rapprochement between O'Neill and the White House resulted in House passage of a $4.9 billion jobs bill, it was pretty much back to business as usual for the Democrats. Thanks to Reagan, thanks to Reaganomics and thanks to the recession, once again it is politically respectable to be a liberal Democrat.

"The president is buying our alternatives," said the speaker, with a grin. "This jobs bill was the bill he called 'make-work legislation.' "

In 1983 the Democrats' focus is the House. By 1984 attention will shift to the Democratic presidential candidates. Until then, O'Neill and his colleagues can, to a great extent, shape the Democratic platform.

The Democrats know what they're against, and are effective in their opposition. Their problem is, what are they for? What is their program?

In a memorandum last January, pollster Peter D. Hart wrote, "The Democrats must play a constructive role in the formulation of policy for the next two years. The voters do not want a legislative stalemate."

Hart also warned that, "A CBS News survey taken on Election Day shows that, by a 3-to-1 margin, voters blame the current economic problems on past Democratic policies rather than current Republican ones. The Democrats cannot return to the programs of the '60s. Instead, they must offer new ideas for the changing realities of the '80s."

The economy will continue to be the No. 1 issue, Hart wrote.

"The Democrats ran in 1982 on the distribution side of the equation--'It isn't fair, it's Republican.' This argument was aimed at the old constituency politics of America and suggested that what really counts is protection of an ever-shrinking economic pie," Hart said.

"Given the realities of 1982, this was enough. In 1983 and 1984, however, the Democrats must look to the production side of the equation and devise a series of proposals aimed at enlarging the economic pie, aimed at growth and the new realities of the high technology revolution taking place."

Hart agreed with the "Atari Democrats," a group of younger neo-liberals who challenged the public works mentality of traditional Democrats in the 97th Congress.

To some extent, the party embraced the "Atari" approach in a televised response to Reagan's State of the Union message in January, advancing such proposals as a "fair tax" revision, commital of 3 percent of the gross national product to research and development and accelerated training of scientists and engineers.

However, beyond the rhetoric, there is little momentum for new ideas.

A modest bill to stimulate math and science education passed the House this week, but overall, House leaders are too preoccupied with jobs and Social Security, the immediate crises, to undertake complex, long-term initiatives to significantly "enlarge the economic pie."

Protectionism is rampant, and a bill requiring that foreign cars be largely built with American-made parts, has the backing of most Democrats.

House members are concerned primarily with "getting reelected and reacting to immediate problems," said Rep. Timothy E. Wirth (D-Colo.), a leading Atari-type. "Getting them to think about new ideas is like pulling teeth."

In September, a Democratic agenda entitled "Rebuilding the Road to Opportunity" was published by the House Democratic Caucus in a lemon-colored volume. It is known on the Hill as "The Yellow Brick Road."

The Ataris don't dispute the need for relief programs. "At a time when the economy and unemployment are so bad, even the old answers seem refreshing," said Rep. Leon Panetta (D-Calif.). "When the walls are caving in, it is hard to talk about dramatic new strategies."

But Panetta warned, "If we're going to win in 1984, we've got to present the American people with strategies going into the year 2000."

The unabashed enthusiasm with which House Democrats have attacked the administration on the Environmental Protection Agency situation goes beyond the constitutional issue. For two years, liberal Democrats have charged Reagan with sabotaging environmental enforcement through budget cuts.

"Now we can show that Reagan is in bed with big business and he's not tending the store," said a high-level leadership aide.

O'Neill is cooperating with Senate Republicans such as Majority Leader Howard H. Baker Jr. (R-Tenn.) and Sen. Paul Laxalt (R-Nev.) In fact, O'Neill said of the president and the jobs bill, "We had to get Laxalt and Baker to stuff it down his throat."

More bipartisanship will follow next week as a Social Security compromise reaches the House floor.

However, in the months ahead, Reagan's flexibility will be sorely tested as the Democrats push for stronger job-stimulating measures, substantial cuts in his military budget and a tax package placing a cap on his third-year tax cut and repealing the indexing of tax rates to take account of the effects of inflation.

"We're not going to stop until the economy turns around and we have a definite economic program out there," O'Neill said last week. "And when we reach November, 1984, the American people will have the message who is responsible for the turnaround. It will be the Democratic Congress.

"It is a war between the president and Congress until our presidential nominee emerges, and he will be our leader."

The usual tensions among Democrats persist, however.

Some of the younger liberals are sceptical of the Ataris.

"A lot of Democrats have gotten mileage out of bemoaning the bankruptcy of ideas," said Rep. James M. Shannon (D-Mass.) "They're full of bunk. We shouldn't be playing the role of throwing up alternatives that aren't going to change policy. We should be putting people back to work."

Some senior liberals are chafing at the compromises on jobs and Social Security, and freshmen who won by running against Reagan are uncomfortable at having to hold hands with him now.

"You can have peaches and cream if you accept tokenism," said Rep. David R. Obey (D-Wis.) "Are we going to wait six or eight months to help these poor devils who have lost their health insurance because they're unemployed?

"I may be looked upon as a troublemaker here, but in my district, they feel I haven't done enough to kick Reagan in the ass."

And the Boll Weevils, the southern conservatives who supported Reagan's program, already are pushing for more military spending and less social-services spending than most Democrats want.

The southern freshmen tend to be more "national Democrats" now, however, and this time O'Neill made sure that his appointees to key economic committees were loyalists.

The leadership also is soothing the impatient with visions of Phases 2, 3 and 4 of the jobs bill, which are to include mortgage relief, health insurance, more public works, job training, aid to local governments and computerized job banks.

But O'Neill is vague when it comes to putting a price tag on future jobs bills. The $200 billion deficit casts a pall over old-fashioned liberal solutions, so that even those who would go back to the old programs advocate scaled-down versions. "Targeting" is the watchword.

"I do not see a New Deal II," said Majority Whip Thomas S. Foley (D-Wash.).