By DAVID JOLLY

PARIS — The European Commission will enact a two-year ban on a class of pesticides thought to be harming global bee populations, the European Union’s health commissioner said Monday.

“I pledge to do my utmost to ensure that our bees, which are so vital to our ecosystem and contribute over €22 billion annually to European agriculture, are protected,” Tonio Borg said in a statement from Brussels, where the commission is based.

Mr. Borg made the announcement after representatives of the 27 E.U. member states failed for the second time in two months to reach a binding agreement on a proposal to ban the pesticides, known as neonicotinoids. The commission had proposed the ban after the European Food Safety Authority recommended in January that use of the pesticides be restricted until scientists determined whether they were contributing to a die-off in bee colonies.

Though a simple majority of 15 nations backed the measure in committee Monday, it failed to gain the required “qualified majority,” which takes into account the relative weight of populations. Britain, which abstained last time, opposed the measure this time. Germany, which also abstained last month, backed it. France and Poland, two of Europe’s largest farming nations, supported it.

Under E.U. rules, Mr. Borg has the authority to move ahead on his own in such cases, as his predecessor, John Dalli, did in 2010, controversially allowing the cultivation of genetically modified potatoes.

Worldwide sales of the pesticides total in the billions of dollars. Two companies that make them in Europe, the German giant Bayer CropScience and Syngenta, a Swiss biochemical company, have said they were willing to finance additional research, but that the current data do not justify a ban.

“The proposal is based on poor science and ignores a wealth of evidence from the field that these pesticides do not damage the health of bees,” John Atkin, Syngenta’s chief operating officer, said Monday in a statement. “Instead of banning these products, the commission should now take the opportunity to address the real reasons for bee health decline: disease, viruses and loss of habitat and nutrition.”

Bayer CropScience called the commission’s plan “a setback for technology, innovation and sustainability,” and warned of “crop yield losses, reduced food quality and loss of competitiveness for European agriculture.”

Europe’s struggle with the question of neonicotinoids and bee health is being closely watched in the United States, where the pesticides are in wide use, and where a bee die-off over the past winter appears to have been one of the worst ever. Beekeepers and environmentalists are suing the Environmental Protection Agency over its approval of the products, which they claim were allowed on the market with inadequate review.

Neonicotinoids are among the world’s most effective and widely used insecticides, and there is significant disagreement as to how much — if at all — they are contributing to the crisis that has devastated global wild and domesticated bee populations.

A plant or seed treated with such a chemical incorporates it into its tissues as it grows, making it lethal to insects that bore into a stem or nibble a leaf. The neonicotinoids are also present in pollen and nectar, and two recent studies have suggested that even sublethal doses might hurt bees.

The U.N. Food and Agriculture Organization notes that 71 of the 100 crops that provide 90 percent of human food are pollinated by bees. Estimates of the value to those crops run to as much as $200 billion annually.

While there are other natural pollinators, including wild bees and flies, current agricultural practices would be impossible without honeybees, and honeybee populations have shrunk alarmingly over the last decade. In the United States, domesticated bee populations are at a 50-year low and falling, and the story is much the same in other countries. Scientists say several factors, including verroa mites and viruses, have contributed to the decline.

In some cases, commercial beekeeping operations are decimated in a matter of days as workers disappear, a phenomenon scientists have named Colony Collapse Disorder. So badly has the bee population been diminished that in California, the important almond crop now requires more than one-third of all the domesticated bees in the United States for pollination.

Some scientists fear that if the neonicotinoids are banned the chemicals that replace them could be worse. But even those who question the linkage between the pesticides and bee deaths say the current state of knowledge is inadequate and that more study is needed.

Under the European measures, which take effect Dec. 1, there will be sharp restrictions on three neonicotinoid pesticides — clothianidin, imidacloprid and thiametoxam — for treating seeds, soil and leaves on flowering crops attractive to bees, like corn, sunflowers and rapeseed, the source of canola oil. The products may still be used on crops like winter wheat for which the danger to bees is deemed to be small. Use by home gardeners will be prohibited.

The two-year ban will allow commission officials to re-examine the scientific studies that were submitted for approval of the pesticides in the first place and “to take into account relevant scientific and technical developments.”

“This gives bees a bit of breathing space to recover,” said Paul de Zylva, an environmental campaigner in London with Friends of the Earth. The time should be used to come up with a comprehensive plan to address the bee crisis, he said, with civil organizations, governments, farmers and companies working together.

The European ban “doesn’t solve all the problems, though, we never said it did,” Mr. de Zylva added. “You’ve got to look at all the problems facing bees, it’s not just pesticides.”

This article has been revised to reflect the following correction:

Correction: April 29, 2013

An earlier version of this article misspelled the name of the mites contributing to the decline of honeybees. They are varroa mites, not verroa.