WASHINGTON - Defense Secretary Robert Gates on Monday called for patience and discretion as President Barack Obama decides how to conduct the war in Afghanistan, urging advisers to speak candidly but privately on strategy.

Gates did not single out anyone in his address at an Army convention in Washington, but his comments followed very public remarks by the top U.S. commander in Afghanistan as well as Obama's national security adviser.

I believe that the decisions that the president will make for the next stage of the Afghanistan campaign will be among the most important of his presidency, Gates said.

So it is important that we take our time to do all we can to get this right. And in this process, it is imperative that all of us taking part in these deliberations -- civilians and military alike -- provide our best advice to the president candidly but privately.

Obama is convening his top foreign policy advisers for a series of meetings to consider options for the eight-year-old war, in the face of rising casualties and souring public opinion. His administration is split over whether to boost U.S. forces or take an alternative path.

Vice President Joe Biden has privately proposed narrowing the mission in Afghanistan, concentrating instead on attacking al Qaeda targets that are based primarily in neighboring Pakistan.

General Stanley McChrystal, the commander of U.S. and NATO troops in Afghanistan, last week told the International Institute for Strategic Studies in London such a strategy would probably be shortsighted.

McChrystal is seeking up to 40,000 more troops and trainers for the Afghan war, according to U.S. officials, and has cautioned that Afghanistan could again become a sanctuary for terrorism if its government were to fall to the Taliban.

National security adviser James Jones said in a television interview over the weekend that he did not see an imminent risk that Afghanistan would fall to the Islamic insurgents. Jones also said al Qaeda's presence there had been sharply reduced.

The debate comes amid a slide in the security situation in Afghanistan, where some 66,000 U.S. forces are stationed.

Afghanistan has been on a different and worrisome trajectory, with violence levels up some 60 percent from last year, Gates said.

In the deadliest battle for U.S. troops in more than a year, eight American soldiers were killed after tribal militia stormed two combat outposts in a remote area of eastern Afghanistan, the military said on Sunday.

Gates, who has been described by aides as undecided on strategy, said he would salute and carry out whatever orders Obama gives him.

(Editing by Paul Simao)