Pentagon leaders on Wednesday signaled a surge in U.S. forces in Afghanistan "sooner rather than later" — a shift that could come later this year as they prepare to cut troop levels in Iraq.

Faced with an increasingly sophisticated insurgency, particularly along Afghanistan's border with Pakistan, defense officials said sending more troops would have a significant impact on the violence.

"I think that we are clearly working very hard to see if there are opportunities to send additional forces sooner rather than later," Defense Secretary Robert Gates told Pentagon reporters. But, he added that no final decisions or recommendations have been made.

His comments suggested an acceleration in what had been plans to shift forces there early next year. And they came as the political discourse on Afghanistan as a key military priority escalated on both Capitol Hill and the presidential campaign trail.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, who recently returned from meetings with commanders in Afghanistan, said they clearly want more troops now.

"It's a tougher fight, it's a more complex fight, and they need more troops to have the long-term impact that we all want to have there," said Mullen, who also met last week with Pakistani leaders.

The Pentagon has been wrestling with how to provide what they say is a much needed military buildup in Afghanistan, while they still have 150,000 troops in Iraq. Gates and Mullen have repeatedly said they would have to reduce troop levels in Iraq before they could dedicate more forces to Afghanistan.

Mullen, who was in Iraq last week, told reporters that he is likely to recommend further troop reductions there this fall. He said he found that conditions in Iraq had improved more than he expected.

"I won't go so far as to say that progress in Iraq from a military perspective has reached a tipping point or is irreversible — it has not, and it is not," Mullen told a Pentagon press conference.

"But security is unquestionably and remarkably better. Indeed, if these trends continue I expect to be able early this fall to recommend to the secretary and the president further troop reductions," he said.

The military buildup in Iraq that began more than 18 months ago has ended, now that the last of the five additional combat brigades sent in by President Bush last year has left the country.

Its departure marks the end of what the Pentagon called the "surge." And it starts the 45-day evaluation period that Gen. David Petraeus, the top U.S. commander in Iraq, told Congress he would need to assess the security situation and determine how many more troops he could send home.

Neither Gates nor Mullen would detail how they intend to juggle the military requirements in Iraq and Afghanistan, they spoke more aggressively about meeting Afghan needs more quickly.

Gates said commanders are looking at moving forces around to take advantage of a small boost in French troops expected in Afghanistan. But he ruled out rolling back some of the promises the Pentagon made to soldiers limiting their deployments to 12 months.

"I think we're looking at a variety of options on how to respond here," Gates said. "I will tell you that I have sought assurances that there will be no return to longer-than-12-month deployments, so that's not something we're considering."

Also, he said he is not aware of any plans to extend the deployments of any U.S. troops currently there.

Gates and Mullen also has strong words for Pakistan, saying Islamabad must do a better job preventing Taliban and other insurgents from crossing the border into Afghanistan to wage attacks.

The absence of pressure from the Pakistanis, Gates said, is giving militants a greater opportunity to penetrate the porous mountain border. He said the key is to further convince the Pakistani government that their country is also at great risk from the insurgents.

Gates said it is an exaggeration to say that the border problems have escalated into a war between Pakistan and Afghanistan. And he also dismissed as untrue suggestions that the U.S. is massing troops along the border preparing to launch attacks into Pakistan.

His comments came as U.S. troops abandoned a remote outpost in eastern Afghanistan where militants killed nine of their comrades this week in a large, coordinated attack. Elsewhere in the frontier region, NATO launched artillery and helicopter strikes in Pakistan after coming under insurgent rocket fire, officials said.

There are currently 36,000 U.S. troops in Afghanistan, including 17,500 with the NATO-led force, and 18,500 who are fighting insurgents and training Afghan forces.