Census Bureau Director Vincent P. Barabba said yesterday he has asked the Justice Department to appeal a federal court ruling that would block publication of 1980 census results until they were adjusted to compensate for persons missed in the actual count.

The ruling was based on a suit by the city of Detroit, alleging that the 1980 census was failing to locate large numbers of city inhabitants, and therefore Detroit and other cities could end up with fewer legislative seats and less federal grant money. Congressional and state legislative seats, as well as grant amounts, are based to a large degree on census population figures. Many other large cities in the Northeast and Midwest have charged that the census has undercounted their populations by failing to count many blacks and Hispanics especially.

Barabba declared yesterday there is no satisfactory and reliable way of estimating -- for jurisdictions as small as a legislative district or other limited divisions of a city or county -- precisely how many people have been missed.

He said that if the Sept. 26 ruling by Judge Horace W. Gilmore is allowed to stand, the Census Bureau will not be able to make accurate projections in time to report to the president by Dec. 31 on state population totals needed for congressional reapportionment purposes. The bureau must inform the states by April 1 of the population of each political subdivision for redrawing district boundaries for congressional and state legislative seats, city councils and the like in time for the 1982 elections.

"We have recommended appeal to the Justice Department because there is no feasible statistically defensible method to measure the census undercount in all sub-state jurisdictions. The structure of the appeal is still under discussion and final decision on whether and how to appeal rests with the solicitor general," Barabba told reporters.

The Justice Department said later it has made no decision on the matter.

Barabba again made it clear he does not believe the undercount is nearly as great as believed by some of the Frostbelt cities, which stand to lose congressional seats because of population declines.

For one thing, he said, some of the initial low figures for complaining cities are preliminary. The Census Bureau is raising these as it returns to check houses initially thought empty but now found to contain people.

Barabba said the bureau is doing a good job of reducing the proportion of uncounted persons in comparison with 1970. Studies after the 1970 census indicated it missed 2.5 percent of the population -- about 5.3 million persons. For blacks, the figure was 7.7 percent, leading to charges that blacks had been robbed of political representation and various forms of federal aid by being undercounted, particularly in the crowded cities of the North. Hispanic groups joined in the outcry.

Barabba said yesterday it appears the 1980 undercount, not including illegal aliens, would be lower than 1970 -- only about 1.4 percent or 3,111,000 persons. He said total U.S. population as of April 1 probably will end up at 223,889,000 persons.

He declined comment on alleged pressure being put on the Justice Department to drop the appeal by politicians from Frostbelt states President Carter must carry to win next month.

The stakes in the dispute are potentially large. About $90 billion in federal grants is given to state and local governments each year, and much of this depends on the population count.

Moreover, a census projection in January estimated Frostbelt states would lose as many as 14 House seats to the South and West, a significant loss of political power.

According to the projection, New York would lose four seats; Illinois, Ohio and Pennsylvania two each, and Michigan, New Jersey, Massachusetts and South Dakota one each. Many of these states contain big cities with large black and Hispanic populations, the groups alleged to be suffering worst from an undercount.