"Georgia and Ukraine are not ready for membership. That is very clear," Rice told a press conference.
"There does not need at this point in time to be any discussion" of the alliance membership action plan (MAP), she added.
The top US diplomat insisted the move did not signal a policy shift. "It really is just a question of how we would execute the Bucharest decision. It is not a change in policy," she said.
But this declaration represented a concession to European demands, as Washington had previously pushed for the two Eastern European nations to join the MAP, which provides de-facto membership to the North Atlantic Treaty Organization (NATO).
Amid opposition from Russia, Germany and France, the United States has cooled its support for a formal path to help Georgia and Ukraine join NATO.
Paris and Berlin maintain that the August war between Georgia and Russia confirmed that allowing the two countries join NATO could exacerbate tensions in the Caucasus.
During an October 2 visit to St Petersburg, German chancellor Angela Merkel indicated it was too early for either Ukraine or Georgia to join the MAP.
With nine former Soviet bloc countries already NATO members, Russia fiercely opposes more Soviet-era Warsaw Pact neighbors like Georgia and the Ukraine even starting the process of joining the western military alliance.
On Tuesday, senior US diplomat Daniel Fried stressed that the controversy was over the MAP -- which is only a "way station" and "mechanism" to achieving full membership -- rather than over the long-term goal of having Georgia and Ukraine join.
"MAP is not the only way to get there," he said.
During an April summit meeting in Bucharest, the 26-member NATO postponed any decision on offering the two nations a MAP until the December foreign ministers meeting in Brussels.
"We believe that the NATO-Georgia Commission and the NATO-Ukraine Commission can be the bodies with which we intensify our dialogue and our activities with Georgia and NATO," Rice said.
She noted that Poland and the Czech Republic never went through the MAP process before joining NATO, and said that Britain had proposed using bilateral commissions instead of the MAP.
On Monday, the Ukrainian presidency admitted Kiev faces challenges in becoming an official NATO member candidate by the December ministerial meeting due to the country's political instability and lack of reform.
"This is a key moment for Europe," Georgian President Mikheil Saakashvili said last week, pressing European members of NATO to back his country's efforts to join the military alliance. "Attributing the status of candidate is not a technical question, it is a strategic choice."
NATO set up the MAP program in 1999 to support prospective members of the military alliance while they carry out the economic, legal, military and political reforms needed to join.