Although he had been backing away from a Senate bid for months after first expressing strong interest last winter, Rep. Peter King (R-N.Y.) made it official Monday: He will not challenge appointed Sen. Kirsten Gillibrand (D-N.Y.) next year.

“The reality is that a statewide Democratic candidate starts the race with a voter registration edge of almost 3 million,— King said in a statement. “To overcome such a large margin, there would have to be intensive media coverage of the race and I would need to raise at least $30 million.

“That is why I would have run if Caroline Kennedy were the Democratic candidate. Her candidacy would have generated the media coverage and financial contributions necessary for me to run a competitive race. That’s all I would have hoped for. Once the race became competitive, it would have been up to me to win it by contrasting my blue collar conservatism with her Manhattan liberalism.

“That race was not to be. Senator Gillibrand generates neither strong support nor opposition. This makes it virtually impossible for me to raise the campaign funds I would need to overcome the built-in Democratic registration advantage and the countless millions of dollars which the Democrats will make available to Senator Gillibrand.

“Without heavy financing, my campaign against her would likely receive little coverage and more resemble shadow boxing than a statewide clash of ideas.—

Despite the fact that some political analysts believe she may be a weak statewide candidate in 2010, Gillibrand has seen a succession of her former House colleagues back away from challenging her in recent weeks, and her once tenuous political position has grown undeniably stronger.

With King out of the picture, former New York Gov. George Pataki remains the Senator’s strongest potential Republican challenger. But he appears to be months away from making a decision about the Senate race. Possibly complicating Pataki’s deliberations is the fact that he is a good friend of Gillibrand’s father, Douglas Rutnik, an Albany lawyer and lobbyist.

On the Democratic side, Suffolk County Legislator Jon Cooper, a wealthy businessman, continues to contemplate a primary challenge. Jonathan Tasini, a writer and labor activist, is already in the race.