Last winter, when Sen. Jay Rockefeller, D-W.Va., vice chairman of the Senate Select Committee on Intelligence, began pushing to have the full committee briefed on the CIA's interrogation practices, Cheney called him to the White House to urge that he drop the matter, said three U.S. officials.

In recent months, Cheney has been the force against adding safeguards to the Defense Department's rules on treatment of military prisoners, putting him at odds with Secretary of State Condoleezza Rice and acting Deputy Secretary of Defense Gordon England. On a trip to Canada last month, Rice interrupted a packed itinerary to hold a secure video-teleconference with Cheney on detainee policy to make sure no decisions were made without her input.

Just last week, Cheney showed up at a Republican senatorial luncheon to lobby lawmakers for a CIA exemption to an amendment by Sen. John McCain, R-Ariz., that would ban torture and inhumane treatment of prisoners. The exemption would cover the CIA's covert "black sites" in several Eastern European democracies and other countries where key al Qaeda captives are being kept.

Cheney spokesman Steve Schmidt declined to comment on the vice president's interventions or to elaborate on his positions. "The vice president's views are certainly reflected in the administration's policy," he said.

Increasingly, however, Cheney's positions are being opposed by other administration officials, including Cabinet members, political appointees and Republican lawmakers who once stood firmly behind the administration on all matters concerning terrorism.

Personnel changes in President Bush's second term have added to the isolation of Cheney, who previously had been able to prevail in part because other key parties to the debate -- including Attorney General Alberto Gonzales and White House counsel Harriet Miers -- continued to sit on the fence.

But in a reflection of how many within the administration now favor changing the rules, Elliot Abrams, traditionally one of the most hawkish voices, is among the most persistent advocates of changing detainee policy in his role as the deputy national security adviser for democracy, according to officials familiar with his role.

At the same time Rice has emerged as an advocate for changing the rules to "get out of the detainee mess," said one senior U.S. official familiar with discussions. Her top advisers, along with their Pentagon counterparts, are working on a package of proposals designed to address all controversial detainee issues at once, instead of on a piecemeal basis.

Cheney's camp is a "shrinking island," said one State Department official who, like other administration officials quoted in this article, asked not to be identified because public dissent is strongly discouraged by the White House.

A fundamental question lies at the heart of these disagreements: Four years into the fight, what is the most effective way to wage the campaign against terrorism?

Cheney's camp says the United States does not torture captives, but believes the president needs nearly unfettered power to deal with terrorists to protect Americans. To preserve the president's flexibility, any measure that might impose constraints should be resisted.

On the other side of the debate are those who believe unconventional measures -- harsh interrogation tactics, prisoner abuse and the "ghosting" and covert detention of CIA-held prisoners -- have so damaged world support for the U.S.-led counterterrorism campaign that they have hurt the U.S. cause. Also, they say these measures have tainted core U.S. values such as human rights and the rule of law.

"The debate in the world has become about whether the U.S. complies with its legal obligations. We need to regain the moral high ground," said one senior administration official familiar with internal deliberations on the issue, adding that Rice believes current policy is "hurting the president's agenda and her agenda."

McCain's amendment would limit the military's interrogation and detention tactics to those described in the Army Field Manual, and it would prohibit all U.S. government employees from using cruel, inhuman or degrading treatment.

Cheney pushed hard to have the amendment defeated. He twice held meetings with key lawmakers to lobby against the measure, once traveling to Capitol Hill in July, to buttonhole Sens. John Warner, R-Va., McCain and Lindsey Graham,R-S.C.

When that tack did not work -- 90 senators supported the measure -- Cheney handed McCain language that would exempt the CIA. Despite Cheney's concerns, Graham said he has not heard any concerns from the CIA suggesting they need an exemption from the McCain amendment. The CIA declined to comment.