WASHINGTON - U.S. lawmakers told President Barack Obama's top advisers on Thursday not enough was being done to combat corruption in Afghanistan, singling out allegations against the Afghan president's brother, whom Defense Secretary Robert Gates acknowledged was a problem.

In a second day of congressional hearings on Obama's decision to send 30,000 more troops to Afghanistan to stem a resurgent Taliban, lawmakers also raised doubts about whether the administration was focused on the larger threat posed by al Qaeda militants across the border in nuclear-armed Pakistan.

Gates said the scourge of corruption in Afghanistan was costing U.S. taxpayers billions of dollars, and he suggested it was now more lucrative to skim off the top of U.S. and international aid contracts than to trade in opium. He vowed not to work with corruption-tainted Afghan officials.

Rising combat deaths and soaring military costs have sapped American public support for the war.

Obama's advisers have faced two days of pointed questions about the likelihood of success after eight years of stagnation, and over his goal of beginning to pull U.S. forces out of the country in July 2011, just one year after the bulk of the additional troops are scheduled to arrive.

Gates said he envisaged July 2011 as the beginning of a gradual, conditions-based process of transferring security responsibilities to Afghan forces. Officials said troop pullouts, if any, may be little more than symbolic at first.

KARZAI'S BROTHER

Democratic Senator Robert Menendez questioned why the United States had invested so heavily in Afghan President Hamid Karzai given August's fraud-marred election and his inability to provide security and basic services to many of Afghanistan's 28 million people.

What has he presided over? Menendez asked.

He's presided over massive corruption, where, you know, anywhere between 20 percent or 40 percent seems to be the going rate of skimming off of the taxpayers' money, Menendez said.

In a second hearing, Representative Gene Taylor, also a Democrat, questioned how the administration could be serious about tackling corruption and drugs in Afghanistan without addressing the alleged role of Ahmed Wali Karzai, the president's brother, in the drug trade.

I'm just not going to talk about that in open session. We are dealing with a sovereign government, Gates said.

Taylor insisted, Someone from the State Department admitted before this committee that it was true.

Gates responded: Well, we have problems with him. There's no question about it.

We are putting tens of billions of dollars into Afghanistan, and too much of it is ending up with sticky fingers along the way, added Gates, a former CIA director.

The New York Times reported in October that Ahmed Wali Karzai received regular payments from the CIA. The agency would neither confirm nor deny the payments.

VAGUE ON PAKISTAN

Obama has been vague about what specific steps are being taken to get Pakistan to root out al Qaeda leadership, as well as Afghan Taliban long suspected of having links with elements of Pakistani intelligence.

Officials said the administration was wary of talking publicly because of sensitivities in Islamabad, whose leaders are wary of being cast as American puppets.

It is not clear how an expanded military effort in Afghanistan addresses the problem of Taliban and al Qaeda safe havens across the border in Pakistan, said Dick Lugar, the ranking Republican on the Senate Foreign Relations Committee.

Democratic Senator John Kerry, the committee's chairman, said what happens in Pakistan, particularly near the Afghan border, will do more to determine the outcome in Afghanistan than any increase in troops or shift in strategy.

Gates singled out the threat posed by al Qaeda leaders operating out of Pakistan with relative impunity.

He said al Qaeda, although weakened, was providing operational support to a range of groups seeking to destabilize Pakistan, including the Taliban and Pakistan-based Lashkar-e-Taiba, the group accused of plotting the assault on Mumbai in November 2008 and other attacks in India.

Gates said al Qaeda was providing Lashkar-e-Taiba with targeting information to help the group plot attacks in India, clearly with the idea of provoking a conflict between India and Pakistan that would destabilize Pakistan.

Admiral Mike Mullen, the chairman of the Joint Chiefs of Staff, said the situation was extraordinarily dangerous.

The Pentagon plans to send the bulk of the 30,000 new troops -- reinforcing the 68,000 already there -- to southern Afghanistan, the Taliban heartland, as well as eastern provinces bordering Pakistan. But U.S. forces cannot cross the border and the few U.S. troops and contractors in Pakistan have a limited training role.

Obama also gave Gates the authority to send up to 3,000 more enablers to help destroy land mines, increase intelligence gathering and treat the injured. Gates said he hoped the additions would not become necessary.

Secretary of State Hillary Clinton said recent Pakistani military offensives against local Taliban groups in the lawless Swat and Waziristan regions were important but were far from sufficient.

But she played down the prospects of immediate action by Pakistan, where anti-American sentiment runs strong.

This is an argument that takes time, she told the committee. There is a great gulf of mistrust.

(Additional reporting by Susan Cornwell and Sue Pleming; Editing by Peter Cooney)

Pakistan Afghanistan Hillary Clinton Barack obama