Mr Cameron said the Tories would back a "no" vote in a referendum
The Conservative Party has urged the government to hold a referendum on the EU Treaty, saying it is "up to the British people to decide".
Leader David Cameron said that, if the Tories gained power before the treaty came into force, they would attempt to reverse last year's ratification.
Ministers were "honour-bound" to hold a referendum on it, as was promised for the discarded EU Constitution.
The government said the Tories would leave the UK "isolated" in Europe.
The Conservatives are launching a poster and internet campaign for a referendum, ahead of the European elections on 4 June.
They have announced they will leave the European People's Party coalition in the European Parliament.
The group is opposed to a referendum and is calling for closer economic integration in Europe, and common immigration, defence and foreign policies.
Mr Cameron and his colleagues argue that the EU (Lisbon) Treaty's contents are largely the same as those of the abandoned European Constitution, on which all the major UK parties promised a referendum at the 2005 general election.
The Tory leader said: "Gordon Brown's flip-flopped on this before. First he was against the constitution, then he was for it; one day he promised a referendum, the next he backtracked.
"While he has chopped and changed, our position has remained exactly the same. We are the only major party to have consistently said that it is up to the British people to decide on our future in Europe.
"That's why we have pledged that if the constitution is not in force in the event of the election of a Conservative government this year or next, we will hold a referendum on it, urge a 'no' vote, and - if successful - reverse Britain's ratification."
The UK is one of 24 EU nations which have ratified the Lisbon Treaty, which aims to streamline its institutions and replaces the failed EU constitution, following a parliamentary vote in June last year.
Mr Cameron said: "Where you stand on the referendum says a lot about your politics. It says a lot about how much you value trust between the government and the governed.
"I believe that if you make a promise in your manifesto, and the country votes on that manifesto, then you are honour-bound to keep that promise."
The document has proved controversial, with unsuccessful attempts in the UK Parliament and the courts to force a referendum on the issue.
The Lisbon Treaty is awaiting approval by the Czech senate and president and Poland's president.
In Germany, despite parliamentary approval, the constitutional court is studying the treaty to judge whether it conflicts with the German constitution.
It will also face a second referendum in the Irish Republic, where it was rejected in 2008.
Under EU rules, the treaty cannot enter into force if any of the 27 member states fails to ratify it.
The Tories argue it is so similar to the discarded constitution that promises to hold a referendum should still apply.
But the government says the two differ and a referendum is not needed as the treaty does not have constitutional implications.
Europe minister Caroline Flint said: "Once again David Cameron is putting Tory Party interest ahead of the national interest.
"We need to work with our neighbours to tackle the global economic crisis, climate change and international terrorism, not retreat to the fringes of Europe.
"David Cameron's policies on the Lisbon Treaty would leave Britain isolated in Europe, at a high cost to British families and businesses."
UK Independence Party leader Nigel Farage said: "David [Cameron] promised that if the constitution was not in force at the time of the general election, a Conservative government would hold a referendum on it, urge a no vote, and reverse Britain's ratification if successful.
"That is a change of position. That is chopping and changing."
He added: "The last Conservative manifesto promised a referendum, no ifs or buts, just like the Labour one did. Now it's been weakened to only if no one else minds very much."