WASHINGTON – The nation’s top defense leaders said Monday that U.S.-led forces were making steady progress in their efforts in a Taliban stronghold in southern Afghanistan but faced stiffer resistance than expected and the operation will take longer than hoped.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, told reporters at the Pentagon that the efforts against the Taliban were ”messy” and ”incredibly wasteful,” as was war in general. ”But that doesn’t mean it’s not worth the cost.”

Mullen said the battle and the broader war can be won with the proper resources and strategy.

”As you’ve all been seeing, we’re making steady, if perhaps a bit slower than anticipated, progress,” Mullen said.

Mullen also expressed regret for a NATO airstrike that killed at least 27 Afghan civilians. It was the third coalition strike this month to kill noncombatants and drew a sharp rebuke from Afghanistan’s government about endangering civilians.

At the same briefing, Defense Secretary Robert Gates defended the top commander in Afghanistan, Gen. Stanley McChrystal, saying McChrystal keenly understands the need to do the utmost to avoid civilian casualties and has made that a top priority. ”I have confidence in his judgment,” Gates said.

For 10 days, U.S. and Afghan troops have been fighting holdout Taliban forces in an effort to secure the southern town of Marjah in Helmand province. ”The situation remains serious but is no longer deteriorating,” Gates said.

On a related subject, Gates said recent arrests of high-level Taliban fighters by Pakistan mark ”real progress” by the Islamabad government and ”another positive indication” of its commitment to stabilizing its border with Afghanistan.

Earlier this month, Pakistani authorities arrested the No. 2 Afghan Taliban leader, Mullah Abdul Ghani Baradar, in the southern Pakistani city of Karachi. Also arrested were a pair of Taliban ”shadow governors” from two Afghan provinces and several other militant suspects linked to al-Qaida and the Taliban.

Gates told reporters that ”what we are seeing is the importance of operations on both sides of the border.”

Asked whether the arrests might help turn the tide in the eight-year-old war, Mullen cautioned against putting too much stock in any single event. He said ”it’s just too early.”

The Afghanistan Council of Ministers strongly condemned the airstrike, calling it ”unjustifiable.”

It said reports indicated that NATO planes fired at a convoy of three vehicles, killing at least 27 people, including four women and a child, and injuring 12 others.