DESPITE GROWING evidence of Pakistani support for the Taliban insurgency in Afghanistan, the Bush administration has so far rejected pleas from Afghan President Hamid Karzai for a showdown with Islamabad's military ruler, General Pervez Musharraf. It is now up to Congress to force administration action by conditioning further U S economic and military aid to the Musharraf regime on definitive measures by Pakistan to shut down Taliban bases in its territory.

The House took a step in this direction in its recent omnibus Homeland Security legislation. Buried in the bill is a ban on further economic and military aid unless President Bush certifies that "the Pakistani government is making all possible efforts to prevent the Taliban from operating in areas under its sovereign control."

But the bill left a glaring loophole: The president can waive the ban if he certifies that "it is important to the national security interest of the United States to do so." More important, it does not cover disguised Pentagon subsidies to the Pakistan armed forces. The Senate should remove or qualify the presidential waiver and include the Pentagon subsidies in the ban.

Since 9/11, the cost of Musharraf's cooperation has reached a staggering $27.5 billion. Economic and military aid has totaled $4.5 billion. In addition, the United States is providing $5 billion in credit guarantees for the purchase of 62 nuclear capable F-16 fighter planes and has orchestrated the postponement of debt repayments to aid donor countries totaling another $13.5 billion.

The subsidies to the armed forces -- $4.5 billion so far and set to reach $7.5 billion in 2008 -- are papered over in Pentagon statistics and have received little congressional scrutiny. What Pakistan gets, nominally as reimbursement for the cost of its counter terrorism operations, is lumped together with other counter terrorism funding. The payments continue to flow whether or not Pakistani forces come out of their barracks in Afghan border areas during a given month.

It is unclear whether Pakistan government agencies are themselves aiding the Taliban or whether they simply look the other way when Musharraf- backed Islamic extremist groups do so. In any case, Defense Secretary Robert Gates said recently that "there are more attacks coming across the border."

The best way for Pakistan to allay suspicions concerning the Taliban would be to give foreign journalists unimpeded access to its border areas. Instead, Islamabad bars journalists from these areas without a government permit, which is routinely denied. New York Times correspondent Carlotta Gall reported that she got to the border towns of Chaman and Quetta without permission and found "signs that Pakistani authorities are encouraging the insurgents, if not sponsoring them." The credibility of her findings was strengthened when Pakistani intelligence agents broke into her hotel room, knocked her to the floor, and took away her computer, notebook, and cell phone, presumably to find out whom she had interviewed.

The key reason for the administration's unwillingness to confront Musharraf is the fear that a showdown would lead to the emergence of a hard line Islamic extremist in his place. But this anxiety is based on the increasingly discredited premise that he is a bulwark against Islamic radicals. The Islamic parties are flourishing under the protective umbrella of military intelligence agencies. Their growth would be slowed if secular political forces had a chance to assert themselves through free elections.

Since the economic viability of Pakistan depends on continued aid, a credible threat to cut it off would alarm both the armed forces and sectors of the Pakistani business and political establishment, forcing Musharraf to tack with the wind. The United States is in a strong bargaining position. In addition to conditioning future aid on an end to support for the Taliban, Congress should press the administration to work for free and fair elections in Pakistan this fall. If Musharraf wants to run for president, he should step down as army chief of staff, and exiled prime ministers Benazir Bhutto and Nawaz Sharif should be permitted to oppose him. A return to civilian rule in Pakistan offers the best hope for neutralizing the disquieting growth of Islamic extremism in Pakistan and Afghanistan alike.

Selig S. Harrison, director of the Asia Program at the Center for International Policy, is author of five books on South Asia.