But Germany's Angela Merkel said a lot of his demands were justified.
The PM is working on a separate plan to boost UK sovereignty aimed at getting sceptical Tories, including Boris Johnson, to get behind his reform deal.
Mr Johnson - who is being touted as a possible leader of the out campaign - has met Mr Cameron at Downing Street.
"I'll be back," he told reporters as he left Number 10, adding: "No deal, as far as I know."
BBC assistant political editor Norman Smith said the London mayor, who is "pivotal" to Mr Cameron's plans, would keep the PM waiting until he had returned from the summit before announcing which camp he would support, although his "no deal" comment was not thought to be a reference to his own concerns about sovereignty.
Sources close to Mr Johnson say his decision on whether to back remaining or leaving the EU is "very finely balanced".
They say the decision by Mr Cameron to try and sell his proposed deal to Mr Johnson underlines how crucial he is likely to be if the prime minister is to win the referendum.
"They are pretty determined to get him on board," the source added.
They have strongly rejected suggestions Mr Johnson's decision is tied to his ambitions to lead the Conservative Party when Mr Cameron steps down.
"His decision is in no way predicated on any leadership question. It's based on what he thinks will be in the best interests of the country," the source said.
Mr Cameron's sovereignty plan is expected to suggest extra powers for the UK Supreme Court to protect UK law from challenges from the European Court of Justice, to assert the primacy of UK law over Brussels.