With a deal that revives a bill requiring the labeling of genetically engineered foods, Connecticut’s legislative leaders Saturday acknowledged a movement that has muscled its way from the scientific fringe to political mainstream.

Senate and House leaders announced a bipartisan compromise that is expected to make Connecticut the first state to require labeling of foods with genetically modified organisms, or GMOs.

It passed the Senate unanimously with little debate and was sent to the House, where the leadership promises final passage before the adjournment deadline of midnight Wednesday.

A week ago, the measure appeared dead. Then a grass-roots group, GMO Free CT, used social media to focus the movement’s ire on Gov. Dannel P. Malloy and House Speaker J. Brendan Sharkey, D-Hamden, whom activists deemed responsible for the apparent defeat.

Senate President Donald E. Williams Jr., D-Brooklyn, said the outpouring made the difference, leading him to stand with Senate Minority Leader John P. McKinney, R-Fairfield, outside the Senate and announce a deal for passage with Sharkey and Malloy.

“We’re very pleased that Connecticut will be leading the nation,” Williams said.

“It’s an extremely important bill,” McKinney said. “We both realized we had a commitment not to let it die.”

Tara Cook-Littman of Fairfield, a self-described PTA mom and food blogger behind GMO Free CT, called the turnaround a pleasant surprise and a significant push for a labeling movement that has changed the food industry in Europe, but not the U.S.

“Honestly, it’s incredibly important,” said Cook-Littman, reached by phone. “This is going to provide momentum for other states.”

The Senate had passed a bill favored by Cook-Littman’s group, only to see the House pass a competing version on May 24 that advocates viewed as deliberately ineffectual. Both votes generated a reaction showing the movement’s political muscle on social media.

Williams and McKinney, who counts Cook-LIttman as a constituent, each found themselves lionized on GMO Free CT’s Facebook page.

“The day the Senate passed the first bill, over a million Facebook hits,” said James Leahy, a former grass-roots organizer who is their Connecticut lobbyist. “I think the depth of their grass roots is unprecedented in my experience.”

Just as Williams and McKinney were praised, Sharkey and Malloy were vilified. The contrast took on an added political dimension, given that McKinney is seriously considering challenging Malloy for governor in 2014.

“When word went out on the House version that wasn’t acceptable, the message went viral,” Leahy said.

Derek Slap, a former TV reporter who is the Senate Democrats’ chief of staff, said the effective use of social-media by GMO Free CT was reminiscent of how gun-control advocates kept up pressure on legislators earlier in the session.

“I think it’s a relatively new phenomenon,” Slap said. “You can organize relatively large numbers of people very quickly and impact public policy.”

It was not unnoticed by Sharkey and Malloy.

Sharkey and the Malloy administration were adamantly opposed to a bill that would make Connecticut the only state with a labeling law, arguing that it could drive up food prices. GMO Free CT urged supporters to call Sharkey and Malloy.

Thousands did.

The House version exempted nearly all local food producers and included a hard-to-meet trigger: The law would take effect only if New York and four other states with an aggregate population of 25 million passed a similar bill.

Under the original Senate bill, the labeling requirement would take effect in 2016, sooner if three other states passed a similar law.

Under the compromise announced Saturday, the exemption for local producers was minimized to cover farm-stand sales and food prepared for immediate consumption.

“Once that exemption was removed, the integrity of the bill was there,” Cook-Littman said. “Then the question was whether we could come to compromise and find a trigger clause the leadership could live with.”

The trigger was changed so that four other states in the Northeast with a total population of 20 million must pass a similar law, and one must border Connecticut. Cook-Littman said the new trigger is reasonable, and Sharkey said it guaranteed that Connecticut would not stand alone.

“We needed to protect two things: One, the consumer’s right to know what’s in their food. The second is the consumer’s right to have affordable food available in the state of Connecticut.”

Malloy issued a statement praising the compromise.

“This bill strikes an important balance by ensuring the consumers’ right to know what is in their food while shielding our small businesses from liability that could leave them at a competitive disadvantage,” Malloy said.