Mr Sikorski, who is a leading contender to become Nato`s secretary-general when the Alliance selects a new chief in April, told The Daily Telegraph that membership for both countries was a "fairly distant prospect".
According to The Daily Telegraph, he denied that Russia, which attaches great importance to thwarting Nato`s enlargement, had achieved a victory.
Ukraine and Georgia were both promised Nato membership at a summit in Bucharest last April. But no timetable was offered and, four months later, Russia raised the stakes by invading Georgia.
Mr Sikorski said that Nato should "maintain the Bucharest consensus" and the "credible promise of membership".
Asked whether the will to admit Ukraine and Georgia existed, however, he replied: "Not at the moment. At the moment, there`s a will to encourage them to reform themselves. But I believe all of our institutions, both the EU and Nato, suffer from enlargement fatigue."
He added: "It`s always harder to enlarge in a recession."
Yet the onset of "enlargement fatigue" did not amount to a victory for Russia. "I don`t have the feeling that Russia has increased its credibility in the last six months," he said. "The Soviet Union never cut off gas supplies to Western Europe. Soviet strategists had a wonderful expression called `correlation of forces` which meant all the factors - material and immaterial - affecting any situation. I don`t believe that either through the Georgia crisis or the gas dispute Russia has improved the correlation of forces to its advantage."
Mr Sikorski, 45, escaped from Communist Poland and was given asylum in Britain in 1982. While studying at Pembroke College, Oxford, he was a member of the Bullingdon drinking club along with David Cameron and Boris Johnson. Mr Sikorski took British citizenship - and diplomats say that he kept his British passport until he was made Poland`s foreign minister in 2007.
During the 1980s, he was a foreign correspondent, covering the Soviet occupation of Afghanistan for The Sunday Telegraph. His firsthand experience of war in Afghanistan gives him a unique qualification for taking the helm of Nato, which now deploys 55,000 troops in the country.
The Alliance`s 26 members will probably choose a new secretary-general at their 60th anniversary summit in April. When Nato Ambassadors meet on Monday, they will begin considering possible candidates, who include Anders Fogh Rasmussen, the Danish prime minister.
As for whether he might be Nato`s next secretary-general, Mr Sikorski replied: "I believe that Nato needs continued leadership from the front. We have a war in Afghanistan that we mustn`t lose. Nato is the most successful alliance in history and that needs nurturing. I believe that the appointment should be made on merit.
"I`m flattered by such suggestions because they imply that Poland is now a regular member and that indeed we`ve made worthwhile contributions to Nato and that therefore we deserve to be seriously considered for the top job."