WASHINGTON - The rapid U.S. build-up in the Afghan war will include more terrorist-hunting forces to chase down militants deemed too extreme to change sides, a top U.S. general revealed yesterday.

"There's no question you've got to kill or capture those bad guys that are not reconcilable," Gen. David Petraeus, the chief of U.S. Central Command, told the Senate Foreign Relations Committee. "And we are intending to do that."

In his first congressional testimony on President Barack Obama's announced plan to send another 30,000 troops to Afghanistan, Petraeus also cautioned that progress probably will be slower than during the build up of U.S. forces in Iraq two years ago, and the war will be "harder before it gets easier."

Petraeus said that in addition to an effort to "reintegrate" Taliban and other insurgents into mainstream Afghan society, there will be a harder push to eliminate the most hardcore extremists.

"In fact, we actually will be increasing our counterterrorist component of the overall strategy," Petraeus said. He provided no details beyond saying that additional "national mission-force elements" would be sent to Afghanistan next spring.

Petraeus appeared to be referring to classified units such as the Army's Delta Force that specialize in counterterrorism and that have been used extensively in both Iraq and Afghanistan. Gen. Stanley McChrystal, who now oversees the Afghan war and was scheduled to testify today before a House committee, previously headed up those units inside Iraq and Afghanistan.

In an interview with PBS's Charlie Rose yesterday, McChrystal cited a formula for success in the counterterrorism effort he led in Iraq, saying the point is to eliminate the middle levels of terrorist networks like al Qaeda rather than focusing on killing only the most senior leaders.

"You cause the network to collapse on itself," McChrystal said. "And that's what I saw happen in Iraq, and that's one of the things we're working on in Afghanistan."

Much of Wednesday's Senate hearing focused on the link between instability in Afghanistan and the presence of Taliban, al Qaeda and other extremist groups in neighboring Pakistan.

Sen. Richard Lugar, of Indiana, the ranking Republican on the committee, said he's confident that allied forces will improve security in Afghanistan, but that the biggest question is whether that will help root out Taliban and al Qaeda havens across the border in Pakistan.

"The president has said that the United States did not choose this war, and he is correct," he said. "But with these troop deployments to Afghanistan, we are choosing the battlefield where we will concentrate most of our available military resources.

"The risk is that we will expend tens of billions of dollars fighting in a strategically less important Afghanistan, while Taliban and al-Qaida leaders become increasingly secure in Pakistan," Lugar said.

Pakistan's stepped-up efforts have been the most effective it has undertaken against internal extremists, Petraeus said. That, he said, is "an important step forward" and does help U.S. efforts to degrade extremist groups in the border region and to defeat the main U.S. target: al Qaeda.

Petraeus is commanding general of U.S. Central Command, which has responsibility for overseeing US military activities in Central Asia, including Afghanistan and Pakistan, as well as the Middle East.