Since 2004, a total of 123 people have been surrendered to the US under the arrangements while only 54 have come here.
Critics argue the treaty is biased against Britain because more evidence is needed to extradite someone from America.
The House of Commons will hold a historic debate and vote on the issue on Monday which will call for reform.
It is understood Tory MPs will be allowed a free vote on the matter even though a victory would pile pressure on David Cameron to act.
That will put him in a difficult corner as the Americans are strongly opposed to any changes.
The US Ambassador to the UK, Louis Susman, yesterday launched a staunch defence of the treaty, insisting it was fair and balanced.
In a private meeting with MPs on the Commons foreign affairs select committee, Mr Susman said he wanted to “correct the myths and inaccuracies” because his country “strongly supports” the arrangements.
He said: “First and foremost, I want to be very clear that we believe our extradition relationship works, it is fair and balanced, and it promotes the interests of justice in both our countries.
“And I believe that having signed the treaty, and having had it tested both through the British justice system and by independent experts, it is now incumbent on the UK government to stand in support of it.”
He said figures quoted in parliament that 24 Britons have been extradited and only one American were “simple not true” and accused critics of using “skewed arguments” for their own agendas.
However, Dominic Raab, the Tory MP who won the right to have Monday’s debate, said: “The government’s latest available data shows that, under the new arrangements, there were 29 British citizens extradited to the US, and just 2 Americans extradited to the UK. I have asked the US Embassy for clarification of their own data, but it is not available.”
The debate is welcome news for the families of Britons facing extradition, particularly Janis Sharp, the mother of Gary McKinnon, the autism sufferer wanted by American authorities to answer computer hacking charges.
Issues to be voted on will include rebalancing the level of evidence needed by each country for an extradition.
The US authorities only need to show “reasonable suspicion” that someone is responsible for an offence while Britain must show the equivalent of “probable cause” to bring an American here.
An official review of the extradition rules by retired judge Sir Scott Baker concluded last month that the Extradition Act was not biased and did not need reform.
And Mr Susman insisted the standard of proof required was the same.
Earlier this month Nick Clegg broke with Government ranks and ordered a Lib Dem review of extradition amid fears the Conservatives will not reform the act.