THE 98th CONGRESS gets down to serious business today after three weeks of fact-finding, fence- mending and otherwise getting organized. The president's State of the Union message, to be delivered this evening, and his budget transmittal, which is scheduled for next Monday, will naturally influence much of the congressional agenda. But Congress already knows about several big items requiring early action.

Both the House Ways and Means and Senate Finance committees have set tight schedules for passing needed Social Security legislation before the Easter recess. Despite the sensitivity of this issue, the prospects for passage of a sensible rescue package are good. Leaders of both parties have signed off on the compromise plan developed by the Social Security commission, and there will be strong pressure from the leadership in both houses for relatively quick agreement.

There is also strong congressional sentiment for legislation to help the jobless. Getting the fast action that is needed, however, may be considerably harder in this area. Sen. Dan Quayle has already held hearings and prepared legislation to link job retraining, education and extended unemployment benefits for the long- term jobless--a good approach. In the House, the Education and Labor Committee plans early hearings on a job-creation measure introduced by Rep. Paul Simon, and the Ways and Means Committee is considering how best to extend unemployment benefits.

Putting all these ideas together in a workable program, and moving such a program to early passage, will require coordinating the efforts of several different subcommittees and committees in each house. That won't happen unless congressional leaders commit themselves to ironing out the jurisdictional disputes that, in recent years, have increasingly impeded congressional action--an effort that is needed in more areas than just this.

Add to these big-ticket items all the many other decisions that putting together a budget will require --especially on defense--and you have a pretty huge workload for Congress. Still, Congress has strong leadership and an influx of new members who seem ready to work hard and cooperatively. There are grounds for optimism.