Downing Street even dismissed the significance of the Starr report. "The Prime Minister doesn't dump people because some report appears on the Internet," said Mr Blair's official spokesman.
He made his remarks as it became clear that the tide of American public opinion is starting to turn in Mr Clinton's favour and the prospects of impeachment are receding.
In the strongest expression of support for Mr Clinton during the sex scandal crisis that has engulfed the White House, the spokesman said Mr Blair would dismiss calls by some Labour MPs for him to distance himself from the beleaguered President.
Some MPs fear Mr Blair may be damaged by this close association with Mr Clinton, especially if the President is forced out of office.
They want him to scrap plans to meet Mr Clinton in New York next Monday.
Downing Street insisted, however, that the meeting would go ahead.
It would take place at a conference of centre-left parties on the global economy and the "third way" policy agenda sought by Mr Blair and Mr Clinton as an alternative to the "old right and left".
Mr Blair's spokesman said it was in Britain's national interest to maintain a close relationship with the leader of the world's most powerful country.
"He sees President Clinton as a very good friend and ally to this country, not least for what he has done on several occasions for the Northern Ireland peace process," the Number 10 spokesman said.
"This report is a matter for the American Congress and the American people.
"The Prime Minister is not a fair-weather friend and whether people like it or not, that's the way he operates."
Never the less, some differences between the two leaders have emerged during their telephone conversations about the world's economic problems.
Mr Clinton, anxious to be seen on the international stage to deflect attention from his domestic crisis, is keen to call a meeting of leaders of the Group of Seven (G7) leading industrial nations.
But Mr Blair, who currently chairs the G7, does not want to summon fellow leaders to a summit unless he is convinced it would achieve tangible results.
Aides say he wants to avoid a "talking shop" meeting which would be dismissed by commentators as a "damp squib".
A decision on whether to call such a meeting would be taken in the next two weeks.