An agreement worked out by the Census Bureau and a federal judge could put off publication of final 1980 census data until next Thanksgiving, delaying congressional and state reapportionment for many months.

The postponement, under the agreement between the bureau and District Court Judge Horace Gilmore in Detroit, would go into effect only if higher courts uphold an earlier Gilmore order that the Census Bureau revise its count to adjust for an alleged undercount of urban minorities.

In a lawsuit, Detroit had alleged that minorities are being undercounted, robbing the cities of political representation and federal aid. Gilmore ordered the bureau to hold up all final results until they had been adjusted for the undercount. The bureau, which disputed charges of a big undercount, contended it had no valid way to make such an adjustment and still meet the Jan. 1, 1981, deadline for certifying state population totals and the April 1, 1981, deadline for reporting the population of political subdivisions of states. These totals are needed to allow reapportionment at all levels of government in time for the 1982 elections.

The Census Bureau, through the Justice Department, is appealing Gilmore's initial order to adjust for the undercount. If it wins the appeal, the population figures can be reported by the originally scheduled Jan. 1 and April 1 dates. f

But the bureau told Gilmore that if it loses the appeal, it will need until next Sept. 30 to adjust the totals for each state and until next Nov. 30 to adjust totals for the political subdivisions of states. Gilmore agreed to allow this additional time.

Attorneys for Detroit reportedly argued that even if the population report is delayed that long, the states can finish congressional and local redistricting in time for the 1982 elections.