The character of the 98th Congress, which convenes Jan. 3, will be decisively affected by the big House of Representatives freshman class. Its 81 members, almost one-fifth the membership, are coming to Washington with one message uppermost on their minds:

The times are too serious for partisanship, political posturing or the pat formulas of the past, be they liberal or conservative.

Although freshmen Democrats outnumber Republicans 57 to 24, tilting the House more heavily against President Reagan and his policies, the great fear of the freshmen seems to be legislative stalemate that could worsen what many of them see as a crisis in this country.

And that fear unites them more than party or ideology divides them.

"I'm by nature conservative," said Alfred A. McCandless (R-Calif.), a former Riverside County supervisor, "but government by nature is a process of compromise. In times like these, you have to move beyond party and think about the good of the country. This is a critical time. The next two years really can determine the future of this country for the next 20 years."

Across the country and across the political spectrum, Bruce A. Morrison (D-Conn.), a former New Haven legal services lawyer, picked up on the same theme.

"We're people who got elected," he said, "because these are serious times and we need solutions."

And Jim Cooper (D-Tenn.), son of a former governor and the baby of the class at 28, said, "I'd be happy to cast one vote for any program that would reduce the unemployment rate or improve the economy, wherever it comes from."

In their pragmatism and lack of ideology, the Class of '82 strikes those who meet its members as being far removed from the Class of '80, the dominantly Republican group that came to Washington with Reagan and took the brunt of the Democratic counteroffensive last November.

When 45 of the 1982 freshmen spent a week in mid-December at Harvard University receiving policy briefings, the contrast struck all who met them.

"These people are much less ideologically self-conscious," said Jonathan Moore, the director of the Institute of Politics at the John F. Kennedy School of Government, and a former official in Republican administrations. "Two years ago, the people we saw here thought there were sure, clean solutions to all our problems, and if you just had enough gumption and integrity, you could put them into effect pretty fast.

"This class," Moore said, "is much more moderate and pragmatic, and not easily classified in political terms. They are very aware of the intractable nature of the problems they face."

Perhaps for that reason, they seemed more earnest than their predecessors about soaking up ideas and information. Mark Talisman, a former Democratic congressional aide who helped establish the freshman seminars at Harvard a decade ago, remarked, almost in awe, "These folks are staying in class," not rushing off to make phone calls or shop.

Francis A. Bator, a professor of economics, said he had given the freshmen "an hour-and-a-half of pretty dense macroeconomics, a lot of it from the blackboard," and had been astonished when "about 15 of them kept me pinned to the wall, outside the classroom, for another hour" when the session ended.

The freshmen impressed each other.

Kenneth (Buddy) MacKay (D-Fla.), a 49-year-old former state senator, said he found his colleagues "quieter, more studious, more thoughtful" than he had expected.

Harley Staggers Jr. (D-W.Va.), 31, a former state senator whose father served in the House for many years, remarked, "I grew up with politics and politicians all my life. There are a lot of dedicated people here ready to make some changes."

Steve Bartlett (R-Tex.), a 35-year-old former Dallas city councilman, said at the end of the Harvard sessions, "There were 11 Republicans up here the first day and all 11 were here at the end. Last time in 1980 , I'm told, half-a-dozen of the Republicans were gone by the end of the first day. We're not easy-answer guys, and in that 1980 class, you had a lot of easy-answer guys."

Similarly, Reagan's fellow Californian, McCandless, said, "Most of us have had considerable experience in state and local government.

"We understand we need practical solutions, not theoretical quick fixes. I'm not being critical, but the class of '80 apparently thought all they had to do was get to Washington and all the problems of Washington would be solved."

McCandless and Bartlett both come from safe Republican districts where Reagan and his policies still ride high.

"The mandate of 1980 may have been softened and confused by the 1982 results," Bartlett said, "but we still have to get government under control.

"I think we've learned, though, that you can't just do it with slogans. Government consumes too much of the nation's resources, but you can't change that by throwing campaign speeches at the problem."

In a similar vein, Michael Dewine (R-Ohio), 35, a former state senator from Columbus, said that to him and many of the others "the old conservative and liberal labels don't make sense any more when it comes to the economy.

"I think you'll find our class a little less ideological and a lot more pragmatic than the 1980 class."

One of the examplars of that approach, among the freshmen, is Ed Zschau (R-Calif.), a successful businessman of 42 who is the first product of the high tech, micro-chip computer industry to reach Congress.

"I come from an industry that has grown like Topsy and has never asked for government help," he said.

"We're non-union and we're largely unregulated. So I didn't come here to get government off our backs, but because I have some experience that I think might be useful in figuring out we can create the new technical and industrial base this country needs."

In some areas, Zschau said, that means less intrusive government. Antitrust policies, for example, "have to take account of the need for companies large enough and strong enough to meet international competition. There's no point in government breaking big companies into small ones, if the small ones can't survive."

But in other areas, he said, there may be a need for bigger government. "Education is one of the key elements for our future success," Zschau said, "and it's distressing we have so little of our resources directed to higher education in technology and the sciences."

To the Republicans, the Democrats did not look like little Tip O'Neills. Dallas's Steve Bartlett said the opposition party freshmen he met "seem more puzzled than liberal. They're open-minded."

But Bartlett quickly added that the new Democrats from his state and elsewhere in the South "can't join the 'Boll Weevils.' That's a no-no. It's the first question most of them were asked when they were starting their campaigns."

Democrats confirmed that less than a handful of the freshmen Democrats are expected to affiliate with the caucus of conservative southern Democrats. James T. Moody (D-Wis.), 47, a former state senator from Milwaukee, noted that the freshmen Democrats had voted unanimously to expel Rep. Phil Gramm (D-Tex.), one of the most prominent Boll Weevils, from his seat on the Energy and Commerce Committee.

But Moody quickly added, "Not more than two or three of the northern Democrats are McGovern liberals. There's not much difference between the northern and southern Democrats in this class. We're all national Democrats."

That view is widely shared. Richard Ray (D-Ga.), 55, a longtime assistant to Sen. Sam Nunn (D-Ga.) and one of the most conservative of the new Democrats, described his class as "a good cross-section of America. Almost all of them are concerned about fiscal responsibility and the deficits."

Marcy Kaptur (D-Ohio), 36, the former Carter White House staff member who recaptured Toledo from the Republicans, said her priorities were probably different from Ray's: "Jobs, Social Security and utility rates." But she added, "There are not a lot of political shackles on any of us, and there's a real desire to work together, even with the Republicans."

While partisan loyalties may assert themselves when the freshmen start working on Capitol Hill, their initial impulse is clearly to put those labels aside, and insist that their elders do likewise, in dealing with what most see as an emergency situation in the economy. "They really think the country can't make it unless there's some willingness to bend ideology and break partisan lines," said Harvard's Moore at the end of his December week with the freshmen.

The outreach occurred at Harvard at all levels from the practical to the intellectual. Bill Richardson, the new Democrat from New Mexico, said he had visited with Zschau, the Republican from Silicon Valley, about getting high tech industry into poverty-stricken northern New Mexico.

"I represent a district that is 40 percent Hispanics and 20 percent Indians," Richardson said. "On Social Security and unemployment compensation, I'm going to be as liberal as anybody you ever met.

"But social spending is not going to solve our economic ills," Richardson continued, "and I was talking to Ed Zschau about an idea I have to create a select committee on industrial development. He could make a great contribution to that."

And Bruce Morrison, the former legal services lawyer from New Haven, said, "Down the road, I'm sure I'll have sharp differences with the Republicans on the role of government, but short-term, there's a lot we can unite on. The experience with Reaganomics has been sufficiently unsuccessful. Most of us, regardless of party, don't want to keep going down that road. And the range of alternatives is not very great.

"There will be broad support for jobs programs of limited size," he said. "Equally there will be broad support for going ahead with the tax cut, to get the stimulus it can provide. There will be a cutting back on defense expenditures, driven not by philosophy but by deficit realities. And you'll find most of us freshmen, of both parties, together on that."

Behind that prediction is one political reality understood by all the freshmen. It was voiced by Frederick Boucher (D-Va.), a 36-year-old former state senator from a perpetually marginal battleground district where coal field unemployment has reached the 25 percent level.

"In 1982," he said, "I was the beneficiary of public frustration with the economy. In 1984, if it's no better, I can be the victim."