An obscure but well-funded campaign to reinvent the Electoral College and elect the president via a national popular vote has alarmed GOP leaders, who have mounted a counterattack with the help of a newly revived nonprofit.

The fight over the Electoral College is “the most important issue in America nobody’s talking about,” Senate Minority Leader Mitch McConnell (R-Ky.) said at a Wednesday forum co-sponsored by the Heritage Foundation and the State Government Leadership Foundation, a GOP-friendly nonprofit that has recently unveiled a new website and ramped up its operations.

The National Popular Vote campaign would replace the Electoral College system, which assigns electors to states based on the size of their Congressional delegations and requires a candidate to win at least 270 of 538 electoral votes to become president. Eight states and the District of Columbia have enacted laws that would instead deliver their Electoral College slates to the candidate who won the most popular votes nationwide. The laws will go into effect when enough states pass similar legislation to break the 270-vote threshold.

The popular vote movement is being spearheaded by “two eccentric businessmen and one of George Soros’ sons,” McConnell declared at the forum, which featured comments by a half-dozen secretaries of state and by election lawyer and former Federal Election Commissioner Hans von Spakovsky.

McConnell added: “They are as well-funded, unfortunately, as they are well-organized, and they are getting close to the finish line.” Advocates of what’s known as the National Popular Vote Compact say they have 49 percent of the 270 electoral votes they would need to change the way the president is elected.

The movement’s leading backers are National Popular Vote and FairVote, a government watchdog group that promotes election equity across the board. National Popular Vote is chaired by John Koza, a computer scientist, professor and software company co-founder, and backed by businessman and philanthropist Tom Golisano, founder and chairman of the payroll and human resource company Paychex.

FairVote’s popular vote plan won over a long list of environmental, labor and civil rights groups in the wake of the contested 2000 presidential election, which delivered the national popular vote to Democratic nominee Al Gore but made George W. Bush president based on electoral votes after the Supreme Court intervened to stop recounts in Florida.

FairVote has received funding from a group now known as the Open Society Foundations, a project of Democrat-friendly investor George Soros, and from Soros’ son, Jonathan Soros. But organizers for both groups said the National Popular Vote plan has support on both sides of the aisle.

“This is, to me, a nonpartisan issue,” said GOP Committeeman Saul Anuzis, former chairman of the Michigan GOP and a consultant to National Popular Vote. “It’s a question of what is the right way to elect a president. In every other office in the land, we elect the person who gets the most votes, from dog catcher to governor.”

Public polling shows strong majorities on both sides of the aisle back replacing the Electoral College with a national popular vote system, FairVote Executive Director Rob Richie said. An October Gallup poll showed 62 percent of Americans favor such a switch.

But McConnell warned that replacing the Electoral College would pave the way for voter fraud and for widespread litigation. He and other speakers warned that registration and voter ID requirements differ from state to state, and a popular vote system would dramatically shift power to major population centers.

Fighting the popular vote movement has emerged as a leading initiative of the SGLF, a project of a powerhouse GOP 527 group known as the Republican State Leadership Committee. Chaired by GOP strategist Ed Gillespie, who was counselor to Bush, the RSLC spent just less than $30 million in the 2010 elections.

RSLC President Chris Jankowski is executive director of the SGLF, which will also spotlight labor, education and immigration issues of interest to state legislators from a small-government perspective.

A spokesman said the group has a budget “well into the seven figures” and that it is expected to double in size by the end of 2012, but he declined to provide specifics.