Gates is in Afghanistan for a two-day visit to get a first-hand feel for changes on the ground since he was last in the country in December.
President Hamid Karzai said he wants U.S. military support, but Gates ruled out permanent military bases in the strategically important country.
Gates says both the U.S. and Afghan governments agree on continued, but reduced American military involvement in Afghanistan after the planned 2014 end of combat operations.
At a news conference with Karzai, Gates said a team of U.S. officials would arrive here next week to begin negotiations over a new compact for U.S.-Afghan security relations after 2014, when all international combat forces are supposed to be gone.
U.S. forces have been in Afghanistan since 2001, and President Barack Obama has repeatedly said the war is not open-ended.
This week's visit is Gates' 13th trip to Afghanistan, and probably one of his last as defense secretary. He has said he will retire this year but has not given a date.
The Associated Press contributed to this report.