MEXICO CITY — El Salvador’s national legislature adjourned Thursday without voting on proposals to allow exceptions to the country’s total ban on abortion, thwarting the first challenge to one of the world’s toughest laws.

The failure of the Legislative Assembly, El Salvador’s legislative branch, to consider two proposals that would have allowed doctors to end pregnancies under limited conditions leaves intact the country’s two-decade-old ban on abortions.

What appeared to be momentum a few weeks ago in favor of relaxing the law was defeated by an alliance of social conservatives and religious organizations who succeeded in convincing legislators in the final days that their vote could have a political cost.

“There are clearly people in leadership who defend this issue no matter what,” said Johnny Wright Sol, an independent legislator who introduced one of the proposals to allow exceptions to the ban. Pointing to the powerful business groups that rallied against changing the law, he said, “There is a lot more tolerance for corruption than there is for discussion on abortion.”