WASHINGTON - Senators from both parties suggested yesterday that the CIA's destruction of videotaped interrogations of two suspected al-Qaeda terrorists could constitute obstruction of justice, carried out as the spy agency's methods were coming under fierce legal scrutiny.

"Burning tapes, destroying evidence, I don't know how deep this goes. Could there be obstruction of justice? Yes," Sen. Chuck Hagel (R., Neb.), a member of the Senate Intelligence Committee and a frequent critic of Bush administration foreign policy, said on CBS's Face the Nation.

The Justice Department and the CIA's inspector general have launched a preliminary inquiry into the controversial destruction of the tapes, which critics charge was an effort to conceal harsh, possibly illegal interrogations.

Sen. Joseph R. Biden Jr. of Delaware, chairman of the Senate Foreign Relations Committee and a Democratic candidate for president, urged Attorney General Michael B. Mukasey to appoint an independent investigator, suggesting the Bush administration could not be trusted to do a thorough job.

"It appears as though there may be an obstruction of justice charge here, tampering with evidence and destroying evidence," Biden told ABC's This Week. "The easiest, straightest thing to do is to take it out of the political realm, appoint a special prosecutor and let them decide and call - call it where it is. Is there a criminal violation? If there is, proceed. If not, don't."

In calling for a special counsel, Biden questioned whether Mukasey was suited to oversee the Justice Department investigation, given his ambivalence during his confirmation hearing over what constitutes torture. "He's the same guy who couldn't decide whether or not waterboarding was torture, and he's going to be doing this investigation," Biden said.

But Hagel and Sen. John D. Rockefeller IV (D., W. Va.), the chairman of the intelligence panel, disagreed with the appointment of a special counsel. Appearing with Hagel on CBS, Rockefeller noted that his committee has already launched an investigation and that CIA Director Michael V. Hayden is scheduled to appear tomorrow to discuss the spy agency's interrogation techniques.

Hayden told his staff last week that the recordings - made in 2002 and destroyed three years later - were destroyed to protect against leaks that might have revealed the identities of the interrogators.

"I don't buy the answer," Sen. Dianne Feinstein, (D., Calif.), another intelligence committee member, said yesterday of the CIA's rationale. Interviewed on CNN's Late Edition, she added that while it has yet to be determined whether destroying the tapes rises to the level of a crime, it was certainly "a big mistake."

The tapes were made under the tenure of CIA director George Tenet and destroyed under his successor, Porter J. Goss, when the agency's harsh methods were coming under fire.

Philip D. Zelikow, who served as executive director of the Sept. 11 commission, has said he believes that the panel, which investigated the terrorist attacks by al-Qaeda, asked the agency for interrogation tapes but none were provided. The commission, appointed by Congress, concluded its work in 2004, when the tapes were still in the CIA's possession.

Meanwhile, political rhetoric escalated this weekend over whether knowledge of the tapes' existence and eventual disposal spilled beyond the boundaries of the CIA.

"I think this leads right into the White House," Biden said. "There may be a legal and rational explanation, but I don't see any on the face of it."

Hagel said it defied logic that senior White House officials would not have been informed of the CIA's intention to destroy the tapes. If they were not, he said, it would indicate "gross malfeasance and incompetency." "It's hard for me to believe that senior members of the White House somehow didn't pay attention to this or didn't know about it," Hagel said. "Maybe they're so incompetent" that they missed it.

Even some of the administration's most loyal defenders were expressing concerns. "I'm troubled by what's been revealed: When the CIA director is unaware of this, the president's unaware of it, the Congress of the United States is unaware of it," House Minority Leader John Boehner (R., Ohio), said on CNN.