LONDON — After 13 years, six scientific opinions and two legal challenges, an insect-resistant type of corn is on the verge of being approved by the European Union. It would be only the third genetically modified crop to be authorized for cultivation in the 28-nation bloc.

Despite clear and at times impassioned opposition from a majority of member countries, opponents of genetically modified crops failed on Tuesday to muster sufficient support to block the authorization under the European Union’s complex weighted voting system.

That left no legal alternative under European rules but to push ahead with the approval, according to Tonio Borg, the European health commissioner, who spoke to reporters after a meeting of ministers in Brussels. Formal approval requires one more step, the go-ahead of the European Commission, the bloc’s executive arm, and Mr. Borg refused to give any timetable for that decision. He is pushing for a mechanism that would allow individual states to ban the growing of biotech crops, but would permit the sale of authorized products throughout the Union.

Supporters of genetically modified crops argue that they offer an unrivaled opportunity to increase yields, but opponents say they pose unknown health and environmental risks.