WASHINGTON -- Trying to save his political career, Deputy Treasury Secretary Roger C. Altman told senators yesterday that he never tried to influence a government investigation into the Whitewater matter or to mislead Congress about it.

Once a rising star in the Clinton administration who appeared on track to succeed Treasury Secretary Lloyd Bentsen, Mr. Altman was grilled for more than nine hours late yesterday and early this morning by both Democrats and Republicans on the Senate Banking Committee, many of whom accused him of having deceived them when he testified before the committee last winter.

In a departure from the Senate's usual courtly manner, the hearing was combative and unrelenting, lurching past midnight with lawmakers on both sides of the aisle assailing Mr. Altman's credibility and none rallying to his defense.

Republican Sen. Phil Gramm of Texas called Mr. Altman's testimony "totally unbelievable," and Pete V. Domenici of New Mexico noted that he was calling the witness "Mr. Altman" rather than "Roger," as he normally would, because "I'm not your buddy right now."

"I can tell," replied a stern-faced Mr. Altman, the No. 2 official at Treasury, then nearing his sixth hour of questioning last night.

Even Sen. Paul S. Sarbanes of Maryland, a fiercely partisan Democrat and Clinton loyalist, was so harsh on the witness that the committee's ranking Republican, Alfonse M. D'Amato of New York, took the highly unusual step of offering to yield his time for questioning to his colleague across the aisle.

After hours of hostile interrogation, Mr. Altman appeared haggard but determined to fight on. Asked around midnight whether he wanted to break for the night, he replied defiantly: "You want to sit here till 7 in the morning, so will I."

Acknowledging the fire he has come under, and that several Republicans have demanded his resignation, Mr. Altman said at the outset yesterday: "I've read that I've already been convicted and sentenced before the trial has taken place."

He apologized to the committee, now in its second week of hearings on the propriety of Whitewater-related meetings between White House and Treasury officials last winter, acknowledging that his testimony in February might have been "too narrow" or "incomplete." But he steadfastly defended his truthfulness and integrity.

"I did not lie to Congress," he said.

Mr. Altman's testimony came on the heels of harsh questioning of the Treasury Department's 28-year-old chief of staff, Joshua L. Steiner, who was rebuked by both Democrats and Republicans for appearing to disavow entries in his own personal diary -- writings that have proved embarrassing and problematic for the administration because of their frank disclosures of behind-the-scenes anxiety over Whitewater.

"It is distressful that a bright, young intelligent man who wrote this diary comes back with some feeble, lame-brain excuses," Mr. D'Amato shouted, pounding his fist.

Although even Democrats appeared deeply skeptical about Mr. Altman's truthfulness in his testimony yesterday, the White House expressed guarded support for him. "At this point, the president has full confidence in his team" at Treasury, Dee Dee Myers, the White House spokeswoman, said yesterday.

One small sign of administration backing was the presence of B. A.

Bentsen, wife of the treasury secretary, who sat directly behind Mr. Altman, along with Mr. Altman's wife.

Mr. Altman, 48, a friend of Mr. Clinton's since their days at Georgetown University, made few mentions of the president or first lady. And he insisted that his contacts with the White House had no impact on the Resolution Trust Corp.'s investigation of Madison Guaranty Savings & Loan, a failed Arkansas thrift with ties to the Clintons. Last fall, the RTC recommended that the Justice Department conduct a criminal investigation of Madison, whose owner, James McDougal, was the Clintons' partner in the Whitewater land deal. Until this spring, Mr. Altman was acting chief of the RTC.

Lawmakers focused much of their attention -- and animus -- on Mr. Altman's testimony before this same committee Feb. 24, when he was asked about "any communications" between White House and Treasury officials regarding Madison. At the time, Mr. Altman understated both the number and substance of such contacts, later amending his testimony in letters to the committee.

The February testimony -- at which Mr. Altman said he knew of only "one substantive contact" Feb. 2 -- was replayed on a videotape yesterday. An ethics agency's report released Sunday said there were at least 40 contacts between White House and Treasury officials.

Mr. Altman acknowledged that his February testimony could have been construed as incomplete and "not as forthright" as it should have been. But he said he never intended to mislead the committee.

He said he mentioned only a single meeting between Treasury and White House officials and failed to note several previous meetings at the White House in the fall, because he did not know of them.

But Mr. Altman's assertion directly contradicted Monday's testimony by the Treasury Department's top lawyer, Jean Hanson. She testified that in late September, at Mr. Altman's instruction, she apprised then-White House counsel Bernard Nussbaum of the RTC investigation into Madison that mentioned the Clintons as possible witnesses.

"I do not believe that to be the case," Mr. Altman said yesterday of Ms. Hanson's account.

He noted that Ms. Hanson sat behind him at the February hearing and didn't correct him. "Just after my response to Senator Bond, I turned to her, and she confirmed my answer," he said.

Mr. Altman's account also was at odds with Monday's testimony by William Roelle, an RTC investigator who said he advised Mr. Altman of the RTC's referral regarding Madison as early as March 1993. "I respect him, but I do not recall it," Mr. Altman said yesterday.

Lawmakers on both sides of the aisle noted the inconsistencies among the various accounts, expressing doubt about Mr. Altman's version.

An exasperated Mr. Sarbanes asked Mr. Altman sarcastically whether there was "some conspiracy at work here on the part of a lot of people" to contradict his account.