Politics, not technical problems, spurred the Reagan administration to rule out any adjustment of the 1990 census to compensate for an expected undercount of blacks and Hispanics, two House Democrats charged yesterday.

Rep. Charles E. Schumer (D-N.Y.), shouting at Commerce Undersecretary Robert Ortner in a hearing, said, "It's shameful {that} the administration's problem with adjusting census figures is not statistical, it's political . . . a raw exercise of partisan politics."

Ortner, who announced the Commerce Department position Oct. 30, shouted back, "That is absurd and outrageous. If you have any evidence, Mr. Schumer, that there was political pressure, political influence and a political decision, I wish you would submit it for the record."

Ortner said political considerations did not enter into the decision, which he said was made by Commerce Secretary C. William Verity. Ortner said he never heard from the White House before the decision "and I haven't heard from them since."

Ortner said the decision was based primarily on the conclusion that "there is no unique model or system that would produce a set of data which all statisticians would support."

House census subcommittee Chairman Mervyn M. Dymally (D-Calif.), who has introduced legislation to require an adjustment of any undercount, said later "there's no question in my mind" that political motives lay behind the decision.

Many specialists believe that an adjustment would help Democrats, perhaps giving them extra House and state legislative seats, because it would raise population counts in Democratic states and sections.

Also testifying yesterday was the former Census Bureau associate director for statistical standards and methodology, who resigned from the bureau because she thought politics had affected the decision on an undercount. Barbara Bailar said that while she had opposed an adjustment of the 1980 census because not enough was known about how to do it, progress on methods of adjustment has been made since then.

Today "the Census Bureau knows how to correct the counts," she said. "The integrity of the census will be irreparably damaged if the official census numbers are uncorrected."

She said that contrary to statements made by Ortner and some other officials, "there is a very broad consensus" in the statistical community "that adjustment would improve the count and decrease the differential."

"Because Dr. Ortner can find a statistician who doesn't agree does not make a case against a consensus. One can still find people who believe the earth is flat," Bailar said.

She added that not a one of 13 statisticians who had submitted a statement opposing an adjustment had actually gone to the Census Bureau and studied materials explaining the new methods for making the adjustment.

Dymally called the Commerce Department decision "premature." He said this was because, under plans developed by the Census Bureau, a final ruling on the technical feasibility of making an adjustment (by taking a 300,000 household survey shortly after the April 1, 1990, census and then comparing the two results for the areas covered) was to have waited until December 1990. That deadline comes just before population counts must be reported to Congress for the purpose of House reapportionment.

Bailar indicated she thought the decision, though announced in October, had been made in August when budget documents developed by Commerce showed that an adjustment would not be done.

Dymally said he intended to "subpoena your records" on the decision, but Ortner said "you don't have to" and said he would cooperate without a subpoena.

"I don't think we have any evidence that it was a political decision," Rep. Constance A. Morella (R-Md.) said.

In 1980, according to Census Bureau studies, the population as a whole was undercounted by about 1 to 2 percent, but blacks and Hispanics by about 5-to-6 percent each. That led to 52 lawsuits to try to force an adjustment, but in the major case, decided last year, a federal court ruled against New York. The court ruled that in 1980 the methods of making an adjustment were not adequate.