Turkish Prime Minister Recep Tayyip Erdogan faces strong pressure from the European Commission during talks Thursday in Brussels to overhaul his country's penal code without including a controversial proposal to outlaw adultery. Turkey's chances of getting a firm date next month to begin negotiations to join the European Union hang in the balance.

The European Commission, the EU's executive body, is scheduled to announce its decision on Turkey's long-standing bid to begin membership talks on October 6. EU leaders are expected to give the final word on the matter at a summit in December.

Commission officials have clearly stated that Turkey can begin the talks only after it has pushed through changes to the penal code, among them measures aimed at preventing torture and strengthening women's rights.

The momentum towards beginning the negotiations, which was spurred by a wide-ranging series of constitutional reforms over the past several months, has now slowed considerably because of Mr. Erdogan's insistence on including a bill to outlaw adultery as part of the penal code reform package, a measure that sparked expressions of concern at the commission. Inclusion of the law is seen by the EU as infusing Islamic law into the Turkish penal code.

Last week, instead of pulling the anti-adultery provision out of the legislation, the Turkish leader withdrew the entire draft law from Parliament, putting it on hold, and causing consternation both in Brussels and among many Turks.

Michael Emerson, an analyst at the Center for European Policy Studies in Brussels, says Mr. Erdogan's party, whose origins lie in political Islam, is split between a faction that wants Turkey to be a full-fledged European democracy and a group that wants to promote a more conservative social agenda in the predominantly Muslim country.

"He's caught between the European Union on the one hand and, in this instance, the conservative factions within his own party," Mr. Emerson said. " Here, I think Erdogan has found himself being obliged to do something in favor of this faction and, probably, not having calculated very well what the European reactions would be. And now he's having to clear up the mess."

A top EU diplomat says that if the Turkish leader is unable or unwilling to make a fast and drastic turnaround on the penal code controversy, the commission may fail to get a consensus on giving the green light to Turkey's entry negotiations. The diplomat says the next few days will tell whether the credibility of the Erdogan government in Brussels has been severely damaged or whether this is just another episode in Turkey's 40-year quest for EU membership.