IF THERE is one striking difference between the freshmen congressmen being sworn in today and their counterparts of two years ago, it is in their degree of confidence. This year's freshmen, of both parties, seem uncertain what should be done about the nation's major problems. They agree that the economy is in doleful condition and that the Social Security system needs to be fixed. They are even, despite party lines and campaign rhetoric, in some agreement about what initial steps should be taken: they are probably willing to back higher taxes to close the deficit and to support some combination of cuts in scheduled benefits and increases in the payroll tax to make Social Security solvent. But they're not sure that such measures will produce the economic prosperity for the nation and the economic security for individuals we all want. Are you?

There's a vivid contrast here with the Republican freshmen in Congress and the Reagan administration of two years ago. The Republicans of 1980 were sure they had solutions for the nation's problems: a three-year 30 percent tax cut, slashes in federal spending, reduced federal regulation, higher defense spending. More than most parties, they succeeded in enacting their platform. But the promised prosperity has failed to arrive. And the administration is still not content with our defense posture.

The Republicans are not the only party with such a record. Democrats came to Congress in 1974 and the Carter administration in 1976 convinced that they had the answers to the nation's problems: price controls on oil, progressive tax reform, national health insurance, lower defense spending. By 1980, they had decided to reverse direction, and today, despite the state of the economy, they are not trying to revive these policies.

So perhaps it's not such a bad sign that this year's freshmen are uncertain that they have the answers. Such uncertainty makes more difficult the passage of any one party's platform. But it also makes it easier for members of parties to compromise and craft new solutions. The painless solutions promised in the position papers of right and left seem to have failed. Now we shall see whether the politicians, in the give-and-take of two-party negotiations, can do better.