The Virginia General Assembly will require a special session next year probably in April, to redraw the state's congressional and legislative districts because government census information has been delayed by court and congressional challenges.

Senate Majority Leader Hunter B. Andrews said yesterday that U.S. Census Bureau data for each of the state's 10 congressional districts will be ready in February at the earliest. The bureau initially had promised to have the figures ready by mid-October, he said, well before the assembly convenes its short, 30- to 45-day session in January. w

"Now, there's no way the House and Senate committees can go to work and get everything done with a short session," said Andrews. He estimated lawmakers would need a month to six weeks to meet due process and notification requirements for public hearings on an reapportionment proposal.

The delays, Andrews added, will complicate other political business in the state, chiefly the spring nominating process for House of Delegates candidates and next fall's contests for governor and other statewide offices.

Virginia and New Jersey, which by law have severe time constraints on the length of their legislative sessions, had been assured priority by the Census Bureau in processing their population statistics. But recent court and congressional challenges to the accuracy of the census information have cast a cloud over the bureau's findings even as census officials are preparing a final report.

Some urban areas, where preliminary findings indicate population decreases, have complained that their minorities were undercounted. And there is a movement in Congress to help up final processing of the census statistics because of concerns that illegal aliens were counted.

Andrews, a Democrat from Hampton, said he expects the assembly to adjourn its short session on schedule and let its House and Senate Committees on Privileges and Elections keep working on reapportionment. Assembly members would return to Richmond for the special session, which Andrews said could last two weeks, when the committees have prepared a redistricting bill for their consideration.

State Sen. Adelard L. Brault (D-Fairfax) suggested yesterday that the assembly could conclude its work in a special session in one day if the committees do some "rough work" in advance, using preliminary population reports.

Since the House and Senate decide their own reapportionment plans independently, Brault said the process should go smoothly provided Republicans in the Democrat-controlled assembly don't challenge the proposal and try to get Republican Gov. John N. Dalton to veto it.

Dalton recently voiced objections to the expense of special sessions called to override his vetoes on other legislation. Citing costs of about $65,000 a day, he has said he is opposed to a constitutional amendment that would mandate veto override sessions each year. He has not, an aide said yesterday, criticized assembly leaders' plans to call a special session for reapportionment.

Brault said the governor's cost estimates were inflated, and that the special one-day veto override session in 1979 cost about $15,000.