WASHINGTON - Social Security benefits for millions of Americans could be put on hold in as few as 10 days if the nation's debt limit is not increased, the Obama administration said today.

In response to a flood of questions from concerned beneficiaries, the Social Security Administration, in consultation with the Treasury Department, has begun advising people that it cannot guarantee payments after Oct. 17 unless and until Congress acts.

"Unlike a federal shutdown which has no impact on the payment of Social Security benefits, failure to raise the debt ceiling puts Social Security benefits at risk," a Social Security spokesman told ABC News.

Neither the Social Security Administration nor Treasury Department would elaborate on specifics of how and when payments could be reduced or cut off. Those contingency plans are still being worked out, a Social Security official said.