BAGHDAD — Iraqi lawmakers adjourned for the summer on Wednesday without passing a crucial election law that many here hoped would solidify the recent, still fragile gains in security. The failure seemed likely to mean the postponement of provincial elections, originally set for October, until next year — polling seen as vital to reconciling the deep-seated tensions among Iraq’s political and sectarian groups.

The decision to go on vacation rather than settle the issue underscored how little progress had been made on the most important recent political question to confront Iraqi leaders, in contrast to the military strides in making Iraq safer than it had been in years. The law was seen as so important to prevent new outbreaks of violence that President Bush, eager to leave office claiming lasting progress in Iraq, had called several Iraqi lawmakers urging them to pass it.