The rhetorical marathon that kept the Senate from going home this weekend involves millions of words about two basic questions: How do you sue to stop discrimination in housing, and what do you have to prove to win?

The filibuster over the bill titled the "Fair Housing Amendment for of 1980" concerns Congress' first attempt to re-write the housing sections -- Title VIII -- of the Civil Rights Act of 1968. The heart of that complex title is a paragraph that prohibits discrimination "because of race, creed, sex, or natural origin in the rental or sale of housing.

While Congress has previously amended the sections of the 1968 civil rights law dealing with discrimination in education and employment, fair housing law has been left to the courts for 12 years. Because the housing business involves so many participants -- buyers, renters, real estate agents, lenders, appraisers and local governments setting zoning regulations, to name a few -- and because the Supreme Court has issued relatively few significant decisions on housing discrimination, current law is so confused that even the experts cannot agree on where things stand.

The legislation now on the Senate floor has already passed the House and was approved this summer by the Senate Judiciary Committee after a year-long battle among liberals and conservatives in the Senate and lobbyists from every corner of the industry. The most important amendment would change the basic mechanism for legal action against landlords or sellers charged with discrimination. Under current law, in most cases the only tool for enforcement is a civil suit brought by the person or group that feels victimized. The federal government's role is limited to conciliation in individual cases, with federal legal action permitted only where a large scale pattern of discrimination can be found.

The House-passed bill, being promoted in the Senate by Birch Bayh (D-Ind.) and Edward M. Kennedy (D-Mass.), would set up a new administrative court where the federal Department of Housing and Urban Development could bring suit against alleged discriminators. While there are various proposals pending for this administrative procedure, the important change is that the government would take over prosecution of cases on behalf of victims.

The real estate industry, with strong support from Sens. Orrin Hatch (R-Utah) and Strom Thurmond (R-S.C.), is working to maintain an enforcement program based largely on private action. The conservatives have agreed to a modification of the Bayh-Kennedy administrative program, but liberals and civil rights lobbyists say this compromise would be so cumbersome as to be almost useless.

The other big issue involves the standard of proof required to show that discrimination has occurred -- how, that is, a court is to determine that a sale or lease fell through "because of" race, sex, etc.

Under civil rights law in areas like education and employment, there has developed an "effects" test. In many cases a person who charges discrimination has to show only that there were no or relatively few minority group members in a certain job or school to establish that discrimination occurred. If the courts find that discrimination was the result, judges will presume that the law was violated.

But in housing law, several federal appellate courts have disagreed about what the victims have to prove. Some use an "effects" test; others have tried to probe the defendant's "intent," finding a violation of law only if the victim can prove the landlord intended to discriminate.

Senate liberals, arguing that it is too difficult to prove intent, want to leave the standard of proof alone. They are betting, in short, that the Supreme Court will adopt an "effects" test for housing.

But Hatch is leading a fight to write the tougher "intent" standard into the Senate bill. There is no such language in the version passed by the House.

If the issues ever come to a vote, Senate leaders say the liberals will win, and the Senate will approve a bill much like the House's.