WASHINGTON - The leading Senate Democrat on military matters said Thursday that he was against sending more American combat troops to Afghanistan until the United States speeded up the training and equipping of more Afghan security forces.
The comments by the senator, Carl Levin, a Michigan Democrat who is the chairman of the Armed Services Committee, illustrate the growing skepticism President Obama is facing in his own party as the White House decides whether to commit more deeply to a war that has begun losing public support, even as American commanders acknowledge that the situation on the ground has deteriorated.
Senator Levin's comments, made in an interview and in the draft of a speech he will deliver Friday, are significant because his stature on military matters gives him the ability to sway fellow lawmakers, and his pivotal committee position provides a platform for vetting Mr. Obama's major decisions on troops.
Underscoring the increasing unease, the House speaker, Nancy Pelosi, said earlier on Thursday that the president would face opposition if he sought to fulfill an expected request from Gen. Stanley A. McChrystal, the top commander in Afghanistan, for more American combat troops.
"I don't think there is a great deal of support for sending more troops to Afghanistan in the country or in Congress," Ms. Pelosi told reporters, emphasizing that she was eager to see a report due from the White House in two weeks on benchmarks to measure the success of the administration's six-month-old strategy.
The White House has begun to indicate that it could be weeks or perhaps much longer before Mr. Obama decides whether to send more troops to Afghanistan.
Administration officials say they want to do a complete review of the effectiveness of the last troop increase, which will put the American presence at 68,000 troops by year's end, an all-time high. They are also digesting a strategic assessment of the Afghan mission that General McChrystal has submitted.
A delay on deciding whether to increase American troop levels would also have the political advantage of pushing down the road a split within Mr. Obama's party while he is trying to build coalitions for overhauling the health care system.
In the telephone interview on Thursday, Mr. Levin said he was not ruling out sending more troops eventually, but rather insisted that the United States try again on a years-old project: finding a way to expand and accelerate the training of the Afghan security forces.
"I just think we should hold off on a commitment to send more combat troops until these additional steps to strengthen the Afghan security forces are put in motion," he said.
Mr. Levin, who returned from a trip to Afghanistan just last week, said that the Afghan national army should be increased to 240,000 troops by 2012 from a current goal of 134,000 by next year, and that Afghan national police forces should grow to 160,000 officers from 96,800 in the same period. These troop goals are consistent with General McChrystal's planning but would be reached a year earlier, the senator said.
Mr. Levin acknowledged that more American trainers would be needed to meet that goal, but he said that he did not know how many. In the most recent deployment of 21,000 American troops, about 4,000 were trainers. The last of those forces will not be in place until November.
In counterinsurgency operations, there are sometimes few distinctions between trainers, support troops and combat forces, a fact that Mr. Levin said he recognized.
He said the United States should send Afghan forces more equipment - including rifles, bullets and trucks - and shift more equipment to Afghanistan from stocks now in Iraq.
Finally, Mr. Levin said the administration needed to adopt a plan to separate low- and midlevel insurgents from hard-core Taliban fighters and commanders. He said the current American efforts to do this had been tentative and halfhearted.
Mr. Levin, who said he intended to outline his proposal in a speech on the Senate floor on Friday, said he explained his concerns in meetings on Wednesday with Secretary of State Hillary Rodham Clinton, Defense Secretary Robert M. Gates and Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff.
Mr. Gates has indicated that he is willing to consider a request for more forces. Separate from any troop request forwarded by the commanders in Afghanistan, Mr. Gates has said he will press for more troops and equipment to protect American, allied and Afghan forces from improvised explosive devices, which are the roadside bombs that have been the leading cause of death and injuries in Afghanistan.
Troops for the mission to counter roadside bombs, which potentially could number in the thousands, would include route- clearance teams and ordnance-disposal units - some of the most dangerous jobs in the military - as well as intelligence analysts and medical personnel. They would be in addition to a substantial increase in the number of armored troop transport vehicles sent to Afghanistan.
While Mr. Levin traveled to Afghanistan last week with two other colleagues, the lawmakers did not agree on all positions.
Senator Jack Reed, a Rhode Island Democrat, said in an interview that he agreed with the need to speed the training and equipping of the Afghan security forces and to reintegrate any Taliban fighters willing to recognize the Afghan government.
Mr. Reed said he was waiting for the analysis by General McChrystal on possible troop increases before making up his mind. "What the president has to do is continually point to the fact that Al Qaeda is operating in the border areas of Afghanistan and Pakistan," he said. "Given the chance to reconstitute themselves and operate in those border spaces, they'll pose a threat to the United States."
Representative Adam Smith, a Washington State Democrat on the House Armed Services and Intelligence Committees who traveled to Afghanistan and Pakistan in the past week, said he also wanted more information before deciding. "But my general position is we have to give General McChrystal what he needs to get the job done," he said.
Other Democrats said Mr. Obama and his military commanders needed to make a more persuasive case to sell the administration's Afghanistan strategy.
"They have a relatively short period of time to show that we're on a path that's going to demonstrate positive results," said Representative Earl Pomeroy, a North Dakota Democrat who visited Afghanistan last week. "This is our last best chance to change things around."
Thom Shanker contributed reporting.