The briefing paper, sent from the Foreign Office to Tony Blair's office, advised ministers to "avoid getting drawn on detail".
The four-page memo, dated 7 December 2005 and first reported on Thursday by the New Statesman magazine, also urged the government to "try to move the debate on" and focus on the importance of cooperating with the US in its "war on terror".
Human rights organisations and legal groups have accused the US of covertly moving prisoners between countries, outside normal legal processes such as extradition.
The process is known as rendition, and as extraordinary rendition when the suspect could be subjected to torture or cruel treatment once transferred.
Government officials said later on Thursday that Jack Straw, the foreign secretary, will make a written ministerial statement to lawmakers on Friday, stressing he has volunteered all available information about US rendition requests.
His decision to further explain the government's position followed a demand from Nick Clegg, foreign affairs spokesman for the Liberal Democrats, that the government make an urgent statement on the memo.
Clegg said: "It is grossly irresponsible that, on a matter of the alleged violation of international human rights, the government's deliberate strategy has been to avoid getting
drawn on detail and to spin the issue away, by moving the debate on," he said.
"This document wholly undermines the prime minister's public assurances."
Shami Chakrabarti, director of the Liberty civil rights group, said she was "incredibly disappointed" the government had opted for "tactical deflection" instead of a robust inquiry into the issue.
According to the memo, the British government was unaware of the number of rendition requests made by the US government. But Blair's official spokesman said on Thursday the government was certain that only three requests had been made - as set out by Straw on 12 December in a statement to parliament.
All were made by former US president Bill Clinton in 1998. Two applications to return detainees to the US were approved, while the request to transport a suspect to Egypt was turned down. None had been made by US President George Bush's administration.
Britain maintains requests were
made under Bill Clinton
"Anything we do in relation to rendition is in compliance with our international obligations".
Several European countries, as well as the European Parliament, are investigating claims that the CIA used European airports for extraordinary rendition.
Condoleezza Rice, the US secretary of state, has insisted the United States complies with the 1994 UN Convention Against Torture and has said that Washington will not transport anyone to a country when officials believe the suspect could be tortured.
Blair has accepted and endorsed her assurances. But human rights organisations say the convention gives the United States a loophole for treatment almost indistinguishable from torture.
In the memo, Britain's Foreign Office also points out the loophole. "... the CAT (convention) prohibition on transfer applies to torture only, not to CID (cruel, inhuman and degrading treatment)".
Sir Menzies Campbell, acting leader of the Liberal Democrats, said this may explain the emphasis on torture in Rice's statement.
"Were you prepared to endorse a statement which may have been carefully crafted so as to allow for the infliction of cruel, inhuman and degrading treatment?" Campbell asked in an open letter to the prime minister on Thursday.
The case of Syrian-born Canadian Maher Arar is one of the most prominent examples of alleged extraordinary rendition. Arar claims he was tortured in Syria after being detained in New York and transferred to Syria by US authorities.
The US Justice Department has insisted that it had information linking Arar to al-Qaida and that Syria promised he would be treated humanely. Syria has denied torturing him.