David Cameron has pleaded with Tory MPs not to act "rashly and prematurely" as he faces a major revolt over calls for an EU referendum.
The Prime Minister said he shared the frustrations of Eurosceptics who have been demanding for years that Britain reclaim powers from Brussels.
But he insisted those issues should not be addressed until the "burning building" of the eurozone debt crisis was under control.
The intervention, in an article for the Evening Standard newspaper, came amid claims that two ministers and more than half a dozen ministerial aides could defy the Government in the Commons.
More than 60 backbenchers have also said they will vote for a referendum on membership of the EU, in the most serious challenge to Mr Cameron's authority since he became party leader six years ago. Conservative MPs have accused the leadership of bullying tactics and bungling party management by imposing a strict three-line Whip on the motion.
There has also been a furious response to efforts by Foreign Secretary William Hague to quell the rebellion, with some backbenchers saying he had "gone native" and abandoned his Eurosceptic values.
Writing in the Standard, Mr Cameron insisted Britain needed to be "single-minded" about getting the EU to "contribute to economic growth, not hold it back". That meant tackling the eurozone crisis, boosting free trade, and controlling budgets in Brussels, he said.
But he argued that an "in-out" referendum was the "wrong approach" at the "wrong time".
The premier said he had made the decision to impose a three-line Whip rather than allow a freer vote because "this issue and Parliament matters".
"The relationship between Britain and Europe isn't some marginal issue," he wrote. "And those of us who believe in the sovereignty of Parliament surely can't argue that some votes don't count."