WASHINGTON - The U.S. general nominated to take charge of the war in Afghanistan pledged on Tuesday to try to minimize civilian casualties even as U.S.-led forces step up operations against insurgents.

Army Lieutenant General Stanley McChrystal told U.S. senators that the war could still be won, but not easily, and U.S. casualties would likely rise.

Civilian Afghan casualties are a major source of tension between U.S. forces and Afghans and their leaders. The New York Times reported on Tuesday that a military investigation concluded that U.S. forces had made significant errors in carrying out some of the strikes in a series of raids in western Afghanistan a month ago.

Citing an unnamed senior U.S. military official, The New York Times said fewer civilians would probably have been killed if U.S. forces had followed rules devised to prevent civilian casualties.

Had the rules been followed, at least some of the strikes by American warplanes against half a dozen targets over a seven-hour period would have been aborted, said the article posted on the Times website.

At the Senate hearing, McChrystal warned that Afghanistan would descend back into civil war and al Qaeda would again use the country as a base if the United States and its allies failed in their mission.

With the appropriate resources, time, sacrifice, and patience, we can prevail, said McChrystal, a special operations officer who currently serves as director of the Pentagon's Joint Staff.

In a surprise shake-up last month, Defense Secretary Robert Gates dismissed Army General David McKiernan as the top U.S. and NATO commander in Afghanistan and picked McChrystal to replace him, saying it was time for fresh thinking.

The United States is pouring thousands of troops into Afghanistan this year as President Barack Obama's administration seeks to turn the tide in a war senior U.S. officials have acknowledged they are not winning.

Washington launched the war in 2001 after the September 11 attacks on the United States, ousting the Taliban rulers.

REVIEW OF RULES

McChrystal said he planned to review the military's rules of engagement and other directives in Afghanistan to ensure everything was being done to avoid civilian casualties.

The perception ... caused by civilian casualties is one of the most dangerous things we face in Afghanistan, particularly with the Afghan people, he said.

We've got to recognize that that is a way to lose their faith and lose their support and that would be strategically decisive against us, he told the Senate Armed Services Committee at a hearing to consider his nomination.

The Afghan government says last month's air strikes in Farah province killed 140 civilians. The U.S. military says 20-35 civilians had been among 80-95 people, mostly Taliban, killed in the attacks.

Afghan President Hamid Karzai has called for an end to U.S. air strikes in his country -- a call rejected by Washington.

As McChrystal testified, the outgoing U.S. commander in eastern Afghanistan said violence there had increased 25 percent this year.

That's the way it is over here. There's some violence that's going to have to be extracted as we go into areas and remove the insurgents, Major General Jeffrey Schloesser told reporters at the Pentagon by videolink from Afghanistan.

But it's the kind of violence that you in fact want because we are getting rid of the insurgents as we do it.

There are 54,000 U.S. troops in Afghanistan now, according to the Pentagon, and that figure is expected to reach 68,000 later this year. Other nations, mainly NATO members, have more than 30,000 troops in the country.

Most of the extra U.S. troops are deploying to southern Afghanistan, the Taliban heartland where U.S., British, Canadian, Dutch and other NATO forces have struggled to establish control.

In the Senate, McChrystal sought to address concerns about prisoner abuse by special operations troops in Iraq that took place while he ran the U.S. Joint Special Operations Command.

I do not and never have condoned mistreatment of detainees and never will, he said.

When we found cases where we thought there was an allegation of mistreatment, we investigated every one and we punished if in fact it was substantiated.

Senator Carl Levin, the committee chairman, said he would have more questions for McChrystal on detainee treatment but no member of the panel indicated opposition to his nomination.

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