WASHINGTON (AP) -- In a potential blow to the antiterror war, Pakistan appears to be preparing to pull troops away from the Afghan border to focus on its own dispute with India, U.S. defense officials said Tuesday.

The Pakistani military presence has been a key element of the U.S. strategy for capturing or killing Taliban and al-Qaida fighters who may have slipped across the border. Without Pakistan's help, the United States has little short-term prospect of finishing off al-Qaida.

American military officials made clear Tuesday they are worried that the dispute between Pakistan and India over the Kashmir region could disrupt the campaign against the al-Qaida in the anarchic tribal areas of western Pakistan.

"Attention and troops that cannot be focused there, because they're focused elsewhere, that's a concern for us, because we need as much assistance as possible in guarding that very porous border," Victoria Clarke, chief spokeswoman for Defense Secretary Donald H. Rumsfeld, told reporters.

"It is a concern when they have to focus attention and people to other parts of the country," she added.

She said U.S. officials "are encouraging Pakistan to remain involved, as they have been, extensively, in the war on terrorism."

Pakistan said last week that it might remove troops from the Pakistan-Afghanistan border region, where they are helping the United States search for al-Qaida and Taliban, and move them toward Kashmir because of the escalating conflict there.

U.S. officials would not publicly say whether Pakistan has moved troops yet, but a senior defense official speaking on condition of anonymity said there are signs that Pakistani troops are preparing to move.

"It's got us concerned," said Brig. Gen. John Rosa, the deputy operations director for the Joint Chiefs of Staff.

Separately, India's defense minister said fighters from Osama bin Laden's al-Qaida network and from Afghanistan's former ruling Taliban have fled to Pakistan-controlled Kashmir.

U.S. officials have been talking with both sides because of what Clarke called grave concern that the India-Pakistan dispute could escalate into all-out war, or even a nuclear exchange.

At the State Department, spokesman Philip Reeker expressed hope that outside appeals to India and Pakistan for calm will produce results.

He noted that British Foreign Secretary Jack Straw is in the region at present and that Deputy Secretary of State Richard Armitage will travel there June 4. Armitage will meet with Pakistani officials June 6 and with Indian officials the next day.

"We're looking for evidence that infiltration has stopped," Reeker said, referring to the support Muslim militants in Kashmir receive from Pakistani-based groups. "The highest priority is to get the tension down."

Dana Dillon, of the conservative Heritage Foundation, said the Bush administration has to focus on U.S. interests in the region.

"We have some troops and personnel deployed in Pakistan," he said. "We don't want them to be nuked. We don't want them (India and Pakistan) to start a war that will escalate to a nuclear exchange."

Clarke and Rosa said the U.S. military has no plans to pull back the thousands of U.S. military personnel in the general region, who could potentially be affected if India and Pakistan fired nuclear weapons at each other.

The United States has troops in Pakistan as well as aboard ships in the northern Arabian Sea. There are more than 7,000 American troops in Afghanistan.

A new analysis by the Defense Intelligence Agency suggests that between 8 million and 12 million people would be killed in a nuclear war between India and Pakistan, according to a U.S. defense official, speaking on the condition of anonymity.

The report presumes that both India and Pakistan successfully use most of the weapons in their nuclear arsenals and target the weapons on populated areas, the official said. The death estimates are in the short-term, and do not include long-term deaths caused by fallout.

Both countries' nuclear weapons are thought to number in the low dozens and have yields at or below 20 kilotons, putting them in the class of the bomb the United States dropped on Hiroshima, Japan, in 1945.

Both can deliver the weapons with small fighter-bombers, such as Pakistan's F-16 and India's MiG-27, or ballistic missiles.