A senior White House official and the former Medicare administrator, central figures in a controversy over the cost of the new prescription drug law, declined to appear before a House committee Thursday, defying Democrats who had sought their testimony.

Citing executive privilege, the White House refused to send Doug Badger, special assistant to the president for health policy, to testify before the House Ways and Means Committee. The former Medicare administrator, Thomas A. Scully, who no longer works for the government, wrote the committee a letter saying he had been busy traveling and would be "unable to appear."

Democrats then tried to persuade the committee to subpoena them, but those motions failed along party lines, by votes of 23 to 16. When Representative Lloyd Doggett, Democrat of Texas, suggested that the panel invite Mr. Scully to appear on a more convenient date, the committee's chairman, Representative Bill Thomas of California, dismissed the idea.

"The chair's reading of Mr. Scully's letter is, He ain't coming," Mr. Thomas declared.

The development infuriated Democrats, who are trying to investigate accusations by the chief Medicare actuary, Richard S. Foster, that Mr. Scully, as administrator, threatened to fire him if he shared his prescription-cost estimates with Congress last year, before the legislation was enacted. Mr. Foster has suggested that Mr. Scully was acting on orders from the White House, possibly from Mr. Badger.

Mr. Foster's figures are important because he calculated that the cost of the prescription drug bill would exceed by about a third the $400 billion that Congress was assuming in preparing the legislation for passage. Had his calculations been widely known at the time, it is possible the measure would have failed, or at least been significantly altered.

On Thursday, Mr. Doggett called Mr. Badger "the Condoleezza Rice for health care." In refusing to send Mr. Badger, the administration invoked the same principle it had cited until Tuesday in refusing to send Ms. Rice to testify in public before the Sept. 11 commission: a "longstanding White House policy," in the words of Alberto R. Gonzales, the White House counsel, that aides who are exempt from Senate confirmation are also exempt from being required to testify before Congress, so that they may feel free to give the president unfettered advice. 

Mr. Gonzales cited this principle in a letter Wednesday to the Ways and Means Committee, in which he said that on behalf of Mr. Badger, he would "respectfully decline the invitation."

As for Mr. Scully, he wrote the panel a two-page letter in which he said he dealt with Mr. Foster "openly and fairly during my entire tenure." He did not address the accusation that he had threatened to fire Mr. Foster, but he did say that when he was administrator, Mr. Foster was not free to communicate directly with lawmakers.

"There is no question whatsoever," he wrote, "that I made it very clear to Mr. Foster, both directly and indirectly, that I, as his supervisor, would decide when he would communicate with Congress."

With Mr. Scully and Mr. Badger absent, Thursday's hearing featured two other officials as witnesses: Jeffery Flick, a former aide to Mr. Scully who now runs the Medicare regional office in San Francisco, and Leslie V. Norwalk, the Medicare acting deputy administrator. It was Mr. Flick who, on Mr. Scully's orders, sent Mr. Foster an e-mail message last year warning him not to release his figures without Mr. Scully's authorization and saying that "the consequences for insubordination are very severe."

Mr. Flick testified on Thursday that "there was a good bit of e-mail traffic" and "some faxes back and forth" between the administration and Congress surrounding Medicare estimates. But when pressed by Representative Pete Stark, Democrat of California, to identify members of Congress who might have been privy to those documents, Mr. Flick could not name any.