A top Census Bureau official who has supervised the government's effort to develop a way to adjust 1990 census figures to correct an anticipated undercount of blacks, Hispanics and others has abruptly resigned her post and will retire.

According to reports in the statistical community, Dr. Barbara Bailar resigned because she believed that political factors may have entered into a decision by the Commerce Department, the bureau's parent agency, that forbids an undercount adjustment. The decision was announced Oct. 30 by Under Secretary Robert Ortner.

"It wasn't the fact that they decided not to adjust but the fact that politics may have entered into the decision," one source said.

Bailar, who is president of the American Statistical Association, confirmed in a telephone interview that she is resigning after 30 years with the bureau. She declined to discuss her reasons, and has made no public statement.

Bailar, as associate director of the Census Bureau for statistical standards and methodology, has supervised a six-year effort to develop an accurate methodology for adjusting the undercount.

The issue's implications cannot be understated: political power and tens of billions of dollars ride on census counts.

Population figures obtained in the census every 10 years determine how many seats each state will get in the U.S. House of Representatives, how much states and localities get in federal grants, and how state legislatures will be redistricted.

If a jurisidiction can show that it has a disproportionately large number of people who were missed in the April 1, 1990, census, an adjustment could bring it more congressional and state legislative seats as well as grant money.

There is a widespread belief that adjustment of the undercount would benefit Democrats and Democratic areas because blacks and Hispanics, who live in areas that usually vote Democratic, are the most severely undercounted groups. An adjustment would add large population counts to these areas, experts said.

Since Ortner's announcement there has been widespread speculation that fear of Democratic gains may have been a factor in the Commerce Department decision, but the Census Bureau has denied it.

According to the bureau, in the 1980 census there was an undercount of 1 to 2 percent for the general population, but for blacks and Hispanics it was about 5 to 6 percent. New York and other jurisdictions that have large black and Hispanic populations may sue to try to force an undercount adjustment after the 1990 census, figuring they would benefit.

Rep. Mervyn M. Dymally (D-Calif.), meanwhile, has proposed legislation to require an adjustment.

According to the methodology worked out under Bailar's direction, the Census Bureau could adjust the undercount by taking a survey of 300,000 representative households nationwide shortly after the April 1 census, and then comparing the results to see how many people were missed the first time.

TerriAnn Lowenthal, staff director of Dymally's House subcommittee on the census, said, "We have an awful lot of respect for Barbara Bailar. If, in fact, her resignation was prompted by dissatisfaction with the decision not to adjust, it is a further indication that the decision was made at higher levels of the administration and not by professionals at the Census Bureau."