"We are in this thing to win," Gates told reporters while traveling late Monday to Kabul, where he planned to meet privately with Afghan President Hamid Karzai and later with troops bearing the brunt of combat.
The secretary's trip to Afghanistan is the first by a Cabinet member since President Barack Obama's announcement last week that he will deploy 30,000 more troops with the intention of starting to bring them home in July 2011.
As Gates took his message abroad, Gen. Stanley McChrystal, the overall military commander in Afghanistan, planned to try Tuesday to convince a skeptical Congress that more troops are needed to fight a growing enemy insurgency. More than 920 U.S. troops have died in the 8-year-old war.
McChrystal's appearance before the House Armed Services Committee starts the first of three days of congressional Afghanistan hearings that are expected to draw hard questions from both anti-war Democrats and conservative Republicans about Obama's stated intention to begin paring down the U.S. role in July 2011.
Gates and other administration officials have described the 2011 date as just the beginning, with the process likely take at least two or three years to complete.
Gates, in a mid-air briefing en route to Kabul, said he believes the U.S. mistakenly abandoned Afghanistan in 1989 as it fought the Soviets and understands Afghan concerns that they will be left alone against the Taliban.
Gates says he will try to assure Karzai and his advisers "that we are not going to repeat the situation in 1989" and that "we intend to be their partner for a long time to come."
He also says he will press Karzai and Afghanistan Defense Minister Gen. Abdul Rahim Wardak on efforts to recruit and train more Afghan soldiers and police officers. McChrystal has set the goal of building the Afghan security force to 400,000 by 2013. There are roughly 94,000 Afghan police officers and 97,000 soldiers today.
Gates' trip came as the Pentagon issued deployment orders for more than 16,000 troops to Afghanistan, the first major installment of the 30,000 reinforcements expected to be in place by next fall.
An infantry battalion of 1,500 Marines from Camp Lejeune will be among the first to arrive later this month, followed by another 6,200 Marines from the North Carolina base and 800 Marines from Camp Pendleton, Calif., deployed next spring.
A 3,400-soldier brigade combat team from Fort Drum, N.Y., will also deploy in early spring. Most of the troops will head toward southern Afghanistan, where anti-U.S. forces have a stronghold and fighting has been heaviest.
On Monday, Joint Chiefs of Staff Chairman Adm. Mike Mullen bluntly told troops at Ft. Campbell, Ky. - including some bound for Afghanistan - that "we are not winning, which means we are losing and as we are losing, the message traffic out there to (insurgency) recruits keeps getting better and better and more keep coming."
The infusion will bring to 100,000 the number of U.S. troops in Afghanistan, the largest expansion of the war since it began.
Obama's plan envisions a burst of soldiers and Marines sent in to tamp down violence, then hand off the mission to the Afghans.
Gates said the U.S. and Afghanistan are trying to address the problem of low recruitment and high attrition among Afghan forces by increasing pay and other incentives. Gates said the biggest challenge is that in many cases, Taliban fighters earn more money than Afghan police officers.
Gates also said the U.S. is prepared to work more closely with Pakistan as soon as the government there expresses a willingness to do so.
"The more they get attacked internally . . . the more open they may be from additional help from us. But we are prepared to expand that relationship at any pace they are prepared to accept," he said.
The drawdown of U.S. forces in Iraq is supposed to liberate billions of dollars of equipment and thousands of troops.
Gates said there is about $3 billion worth of equipment in Iraq, and that $2 billion of it will be transferred or given to the Iraqis by September 2010. In some cases, he said, it will be less expensive for the U.S. to buy new equipment for troops in Afghanistan than to try to move it from Iraq.