Washington ? The Health and Human Services inspector general is launching an inquiry into whether Bush administration officials committed any wrongdoing last year by withholding from Congress internal analyses showing that Medicare prescription drug legislation the White House supported would cost significantly more than lawmakers believed.

President Bush’s top health adviser, HHS Secretary Tommy Thompson, said Tuesday he had asked the department’s investigative arm to examine the failure to disclose such cost estimates and alleged threats made to the government’s chief analyst of Medicare costs that he risked being fired if he sent lawmakers that information.

“There seems to be a cloud over the department because of this,” Thompson said. He predicted the agency would be exonerated. But he also lashed out at a recently departed top assistant, blaming the episode on Thomas Scully, who ran the Medicare program for three years and was a key administration negotiator over changes to the program that narrowly passed Congress in November.

The internal inquiry into the handling of the cost estimates was part of a broad damage-control strategy HHS officials have begun mounting to defuse accusations that the administration has put politics above accuracy on an issue that Bush cites in his re-election campaign as a prime domestic achievement.

Thompson and his lieutenants also sought Tuesday to tamp down complaints from Democrats that a video the administration recently sent to television stations about the new Medicare prescription drug benefits was misleading.

The GOP had anticipated that the law’s passage would give them a potent political victory. Instead, it has produced a partisan, election-year battle and polls indicating that older Americans covered by Medicare are largely unconvinced that the changes will help them.

The controversy escalated late last week when the Medicare program’s longtime actuary, Richard Foster, said Scully had threatened to fire him in June if he answered lawmakers’ requests for data about the fiscal implications of the Medicare bill. The administration did not disclose until January that its calculations suggested the law would cost $534 billion over the next decade, compared with the Congressional Budget Office’s prediction of $395 billion. Foster said his analyses as early as last spring consistently had shown the bills would cost $500 billion to $600 billion.