With the nation''s top military officer calling the situation in Afghanistan dire, President Barack Obama soon may face two equally unattractive choices: increase U.S. troops to beat back a resilient enemy, or stick with the 68,000 already committed and risk the political fallout if that''s not enough.

Adm. Mike Mullen on Sunday described the situation in Afghanistan as "serious and deteriorating," but refused to say whether additional forces would be needed.

"Afghanistan is very vulnerable in terms of (the) Taliban and extremists taking over again, and I don''t think that threat''s going to go away," he said.

Army Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, is completing an assessment of what he needs to win the fight there. That review, however, won''t specifically address force levels, according to Mullen, the chairman of the Joint Chiefs of Staff.

But military officials privately believe McChrystal may ask for as many as 20,000 additional forces to get an increasingly difficult security situation in Afghanistan under control. And one leading Republican is already saying McChrystal will be pressured to ask for fewer troops than he requires.