Accelerate Long Island, a nonprofit organization trying to build a network of high-tech startups, has forged a potentially lucrative alliance with the region's largest venture capital firm, Topspin Partners.

The partnership, expected to be formally announced Thursday, equips the three-year-old nonprofit with a direct conduit to introduce aspiring entrepreneurs from local research facilities to the $213- million fund.

"Accelerate Long Island is spending a lot of time and effort to dig out promising technology to commercialize," said Leo Guthart, Topspin's co-founder and chief executive. "The next step is sifting through all the work they have done and picking the ones that we think are worthy of funding."

Officials have hoped for decades that Brookhaven National Laboratory, Cold Spring Harbor Laboratory and other local research facilities would give rise to startup companies to replace high-paying jobs lost in the decline of the local aerospace industry. The effort, however, has not borne much fruit.

Leaders at Brookhaven, Cold Spring Harbor and elsewhere joined forces to found Accelerate Long Island in 2011, hoping to jump-start the movement. Mark Lesko, who became the group's executive director last year, said Topspin fills a significant void in the Island's hope to become a launchpad for high-tech entrepreneurs.

"My conclusion after doing this for a little over a year is that the big missing ingredient out here is capital," Lesko said. "So we felt strategically like it was important for us to align with the largest source of capital on Long Island."

As part of the alliance, Accelerate Long Island has moved its Melville headquarters to Topspin's office in Roslyn Heights. Guthart and Steve Winick, a Topspin managing director, will join the nonprofit's board of directors. And Topspin will participate in an investment group created to match early-stage grants from Accelerate Long Island.

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The nonprofit received $500,000 in state funds in 2011 to write grants of up to $50,000 to fledgling companies. But Accelerate Long Island has yet to award any of that money. Lesko said the organization is undertaking due diligence with eight startups and plans to announce grants soon.

Topspin was established in 2000 by Guthart, a former chief executive of Ademco Security Group, and James Simons, an ex-Stony Brook University math professor who founded Renaissance Technologies, an East Setauket hedge fund with $15 billion in assets.