On what was supposed to be the last day of the legislative session Virginia's House of Delegates tonight passed a fifth plan to redistrict the state, but by then the state Senate, which must approve the plan before it can be signed by Gov. John N. Dalton, had gone home.

As a result, the General Assembly of 1981 must convene again Wednesday morning hours before the newly elected members of the 1982 Assembly are sworn in to approve a a two-part plan that is a compromise between the Democratic leadership and the Republican governor and a political victory for House Majority leader Thomas Moss (D-Norfolk).

"The governor made me an offer I couldn't refuse," said Moss, who kept Norfolk's five delegate seats in one multimember district in option A of the plan, while the rest of the state was cut into districts represented by one delegate. Under plan B, included in the redistricting bill in case the Justice Department or a federal court rejects plan A, calls for the entire state to be represented by members from single districts.

Civil rights groups that were successful in getting earlier multimember redistricting plans rejected by Justice and the courts as racially discriminatory or constitutionally unrepresentative said today they would go to court against option A and B, both of which they say are racially discriminatory.

"The likelihood of the court accepting a plan so obviously irrational is small," said Judy Goldberg, a lobbyist with the American Civil Liberties Union of Virginia. "It is ludicrous. It's a fantasy."

"You'll be after me in court, you've been doing it for years," said Moss to Goldberg in a corridor of the state capitol building. "I'm not worried about that."

Goldberg and black leaders in the state have argued that a multimember district in Norfolk discriminates against blacks. Norfolk, which has a black population of 35 percent, has one black in the five-member delegation. Moss and his colleagues in Norfolk argue that blacks can retain influence over all five delegates by keeping the multimember plan.

That same argument was used by delegates from Richmond, Newport News, Alexandria and three other cities that wished to keep multimember districts. Only Moss had the political influence to save Norfolk, where most of the delegates live close enough to each other to make single-member districts difficult to draw without placing two or more incumbents in the same district.

This is the 13th time the entire state legislature has gathered to deal with redistricting and the fifth plan approved since the General Assembly began changing political boundaries last March to comply with the 1980 Census figures.

The first plan was rejected by Justice. The next one was scuttled by a three-judge panel in federal court. Gov. Dalton--once by veto and once by technical maneuver--prevented the last two plans from getting far enough to be tested by federal authorities.

Virginia has already spent more than $1 million on the redistricting task that some members have jokingly compared to the Greek myth of Sisyphus, who was condemned by the gods to forever roll the same boulder up the same hill.

Del. Mary Marshall (D-Arlington) voted tonight to pass the plan while acknowledging that she did not think option A, giving Norfolk exclusive rights to a multimember district, had a chance of being approved by Justice.

"If we fail to enact something before the 1982 session, we will crucify our nice shiny new Democratic governor," said Marshall, referring to Charles S. Robb, who will be inaugurated Saturday. "Why should he get stuck with mopping up the rather unsavory pieces?"

Del. C. Jefferson Stafford (R-Giles) provoked one of the few laughs in an otherwise grim afternoon when he berated his colleagues in the House for the poor workmanship done during the redistricting sessions.

Citing Oliver Cromwell's dismissal of an English parliament in the 17th Century, Stafford said, "You have sat here too long for any good you are doing . . . . In the name of God, go."