WASHINGTON (CNN) -- Defense Secretary Robert Gates is leaning toward the view that a significant number of additional combat forces will be needed for the war in Afghanistan, sources told CNN Thursday.
Defense Secretary Robert Gates will likely agree that more troops are needed in Afghanistan, sources say.
Gates is inclined to back Gen. Stanley McChrystal, the top commander in Afghanistan, in pursuing a form of the counterinsurgency strategy, the defense and administration officials said.
Both officials stressed that Gates is not necessarily supportive of sending all the additional forces McChrystal would want, which sources have said could be as many as 40,000 troops. But they said Gates will likely agree with Joint Chiefs Chairman Michael Mullen, who told Congress last week that he expects more troops will be needed.
At the same time, another senior military official separately told CNN any final strategy Gates endorses may not be solely a counterinsurgency one.
President Obama convened his national security team Wednesday for a wide-ranging, three-hour discussion about how to proceed in Afghanistan.
The meeting was described by the White House spokesman as "robust," with the president hearing from 17 people.
"We had an opportunity to get a fairly in-depth intelligence assessment on what's going on in Afghanistan and Pakistan, and to assess individually where we are in each and what's changed since March" when the president decided to send an additional 21,000 troops, White House Press Secretary Robert Gibbs said.
One senior administration official who attended the meeting said the discussions ran the gamut of scenarios. The source did not want to be identified because he was not authorized to speak on the record about the meeting.
There was not a lot of "sniping," the source said, describing it as a "good meeting."
The source said different strategies were aired and there was the ability to "shine some daylight" on different plans, questioning assumptions and viability.
Vice President Joe Biden's idea of pulling back from a counterinsurgency strategy of protecting the Afghan population and instead focusing on using drones to go after al Qaeda was scrutinized, the source said. Opponents explained their objections to that strategy, while proponents detailed their support. It was illuminating to see that it was not quite so simple to just pull back and send drones, said the source.
McChrystal and others explained their counterinsurgency strategy and answered questions about how additional troops might change the mission and where those additional numbers might be found.
In addition, several sources said Secretary of State Hillary Clinton said she was concerned about having enough troops present in Afghanistan to support the Obama administration's civilian efforts, suggesting she may be leaning toward more troops as well. But, the sources said, Clinton made clear that she favors a more detailed examination of the mission before a decision on troop levels is made.
In London, England, on Thursday, McChrystal said he believes the situation in Afghanistan is serious and deteriorating. McChrystal suggested that focusing on al Qaeda, Biden's proposed strategy, would not be enough.
"I absolutely believe that al Qaeda and the threat of al Qaeda and Taliban senior leadership are critical to stability in the region," McChrystal said in a speech to London's International Institute for Strategic Studies. "But I also believe that a strategy that does not leave Afghanistan in a stable position is probably a shortsighted strategy."
Gen. David Petraeus, who as head of U.S. Central Command makes the final military decision on McChrystal's request, said the strategy is being reassessed and no decision on additional troops has been made.
"I have not yet endorsed the resources" requested by McChrystal, Petraeus said while speaking at an event in Washington.
CNN's Elise Labott and Adam Levine contributed to this story.