WASHINGTON - Gen. David Petraeus disclosed yesterday that American commanders have requested the deployment of an additional 10,000 U.S. troops to Afghanistan next year, but he said the request awaits a final decision by President Obama this fall.

Petraeus acknowledged that with 38,000 troops in Afghanistan, the ratio of coalition and Afghan security forces to the population is projected through 2011 to be significantly lower than the 20 troops per 1,000 people prescribed by the Army counterinsurgency manual he helped write.

"It is a concern," said Petraeus, who oversees the wars in Iraq and Afghanistan as head of U.S. Central Command. "If you assume there is an insurgency throughout the country . . . you need more forces," he told the Senate Armed Services Committee.

The testimony came as Taliban suicide bombers disguised in army uniforms detonated a car bomb and stormed an Afghan government office yesterday, killing 13 people. The attack on Kandahar's provincial council office killed seven civilians and six police officers, officials said. Seventeen people were wounded.

The multiprong raid mirrored an attack in Kabul in February when extremists assaulted three government buildings, killing 20.

Petraeus noted during his testimony that the Taliban and other insurgents were growing stronger and that the U.S. military would fight "relentlessly and aggressively" against extremists. Defense officials say the Pentagon is seeking as much as $3 billion over the next five years to improve Pakistan's ability to fight insurgents in the mountainous Afghan border region.

Michele Flournoy, undersecretary of defense for policy, told the Senate panel that the new strategy for Afghanistan and Pakistan was based on a plan to concentrate forces in "the insurgency belt in the south and east," rather than throughout Afghanistan.

Obama "doesn't have to make a decision until the fall, so the troops would arrive, as planned, in 2010," she said. The number of troops is projected to rise to 68,000 with deployments scheduled for this year. If the additional 10,000 troops are approved for next year, the total would rise to 78,000.

Flournoy said the administration also remained open to further increasing the size of the Afghan National Army and the police force, which currently plans to increase their ranks to 134,000 and 82,000, respectively, by 2011.

Petraeus warned that "reversing the downward security spiral" in Afghanistan and Pakistan would be possible only with a "sustained, substantial commitment" of military and civilian resources. "There will be nothing easy about the way ahead in Afghanistan and Pakistan," he said.

Senators questioned Pakistan's willingness to crack down on insurgent safe havens in the western tribal areas.

Petraeus said that while the Pakistan had stepped up efforts, "considerable further work is required" and could be accelerated with U.S. military assistance. Still, he said, cooperation in intelligence must be "done very carefully" because Pakistan's intelligence agencies have divulged sensitive information in the past.

This article contains information from the Associated Press.