The Commerce Department yesterday rejected the recommendations of racial minorities and large cities that it adjust its 1990 census to include people who are missed in the national head count.

"We don't play with the numbers," Commerce Undersecretary Robert Ortner said. "The department does not intend to adjust the 1990 decennial population count for purported undercount and overcount of population subgroups.

"Adjustment may create more problems than it solves and may divert resources needed for enumeration," Ortner said.

The department's Census Bureau has been under considerable pressure, particularly from officials or large cities and minority groups who contend many of their members are missed in the census, to adjust the 1990 count.

The Constitution requires that the national census be taken every 10 years so the figures can be used in congressional redistricting. Critics say the undercount results in underrepresentation in Congress.

These groups also said they fail to get their share of federal funds and other programs organized according to the population figures.

The Census Bureau has estimated that its 1980 count missed between 1 and 2 percent of all Americans, but that as much as 7.5 percent of black males may have been missed.

Rep. Mervyn M. Dymally (D-Calif.), chairman of the House census subcommittee, has offered a bill to require the bureau to find a way to compensate for the uncounted.

Nonetheless, Ortner said his department has concluded that the problems created by making an adjustment would be greater than the problems it might solve.

Even statisticians cannot agree on a method of making an adjustment, he said, and any post-census survey would likely be less accurate than the census.

"We want the public to respond as close to 100 percent as possible. If we tell them we are going to adjust, many people may conclude 'why bother' answer the census" when it is taken on April 1, 1990, Ortner said.