David Cameron says the draft deal aimed at keeping Britain in the EU will deliver the "substantial change" he has been demanding to how it is run.
But the UK prime minister said there was "detail to be worked on" before a crunch summit on 18-19 February.
The deal, which includes an "emergency brake" on migrant benefits, paves the way for the UK's EU referendum to take place as early as June.
EU exit campaigners said it did not come close to what the PM had promised.
But the prime minister says it is a deal "worth fighting for" and he is launching a fresh round of diplomacy to persuade other EU leaders to sign up to it.
The draft deal was published by European Council president Donald Tusk after months of negotiations between UK and EU officials.
David Cameron says the draft deal aimed at keeping Britain in the EU will deliver the "substantial change" he has been demanding to how it is run.
But the UK prime minister said there was "detail to be worked on" before a crunch summit on 18-19 February.
The deal, which includes an "emergency brake" on migrant benefits, paves the way for the UK's EU referendum to take place as early as June.
EU exit campaigners said it did not come close to what the PM had promised.
But the prime minister says it is a deal "worth fighting for" and he is launching a fresh round of diplomacy to persuade other EU leaders to sign up to it.
The draft deal was published by European Council president Donald Tusk after months of negotiations between UK and EU officials.
What those who want the UK to leave the EU say
Richard Tice, co-founder of Leave.Eu, accused Mr Cameron of "trying to deceive the British people by saying that there's substantial change - there is nothing except a restatement of the existing status quo".
The Vote Leave campaign said Mr Cameron had broken a key Conservative manifesto pledge to insist on a four year ban on in-work benefits, saying that the ban was now conditional.
Former defence secretary Liam Fox said the proposals did not "come close" to the changes voters had been promised.
UKIP leader Nigel Farage said Mr Cameron's deal was "pathetic" and "hardly worth the wait".
Donald Tusk's response
President of the European Council Mr Tusk said the package was "a good basis for a compromise", adding that "there are still challenging negotiations ahead - nothing is agreed until everything is agreed".
Conservative reaction
Two of the favourites to succeed David Cameron as Conservative leader, Boris Johnson and Theresa May, have also been touted as possible figureheads for the campaign to leave the EU. Mr Johnson, the London mayor, said he had "doubts" about the red card mechanism, saying there was "much, much more that needs to be done" on European reform.
Home Secretary Mrs May also said more needed to be done, but added: "This is a basis for a deal." BBC political editor Laura Kuenssberg said she appeared on the verge of backing the prime minister and that her reaction would come as a blow to the Out campaign.
Analysis by BBC Deputy Political Editor James Landale
Mr Cameron may have to spend the next two weeks twisting arms in Europe, there may be no guarantee of a deal and everyone is agreed that nothing is agreed until everything agreed.
But the prime minister is already in campaign mode, bouncing around tiggerishly in his shirtsleeves, selling his deal almost as if it had been agreed. Read more: James says Cameron in campaigning mode
Will other EU nations accept it?
The BBC's Europe Editor Katya Adler says: "My first instinct is that this is something everyone can work with.
"Eastern and Central European countries will continue to complain about the suspension of migrant in-work benefits.
"They are likely to argue that the EU has sold its principles down the river in an attempt to keep the UK in the EU.
"However it can be argued from this text that the so-called 'emergency brake' is not discriminatory because it's available for any country to use." Read more: Katya's blog in full.
