By Stephen M. Silverman
Updated September 09, 2003 08:40 AM

It seemed like the worst-kept secret in New York on Tuesday: Simon & Garfunkel were holding a press conference “for a very special announcement,” but every invitee knew the purpose of the gathering.

The place: The Bottom Line, the downtown music club that launched many careers, including those of two Queens, N.Y.-bred folk artists named Paul Simon and Art Garfunkel, whose 1963-70 partnership generated five Grammys and record sales of 40 million copies.

The announcement: The pair will hit the road for “Old Friends — The 2003 Concert Tour,” the first S&G concert tour in 20 years, kicking off Oct. 18 in Auburn Hills, Mich., and traveling to U.S. arenas through mid-December.

Encouraged by their reunion performance at this year’s Grammys, the off-again, on-again friends will travel to 30 cities in all — with date and location specifics to be made available in local newspapers. Tickets go on sale Monday.

Meanwhile, eight days before the first concert, a two-disc “Essential Simon & Garfunkel” will be released by Columbia/Legacy, which describes the CD set as a collection of the duo’s biggest hits and fan favorites.

Taking to the stage at the packed press conference, Simon, wearing a rust-colored T-shirt and jeans, and Garfunkel, wearing an open plum-colored shirt (with matching purple necktie dangling over his collar), sang “Old Friends,” from their groundbreaking 1968 album “Bookends.”

It was followed by “Homeward Bound” and, to close their half-hour appearance, a rendition of “The Boxer.”

Admitting to their contentious relationship — which led to the dissolution of their act — Simon, 60, called their past differences “just squabbles, that’s all they were, (and) that’s all behind us.”

“This is a deep, old friendship, going back many, many years,” said Garfunkel, 61. “Our moms know each other.”

He also admitted that time can take its toll, and that he looks forward to the “fun of going up to the high notes” on “Bridge over Troubled Water.”

Both claimed a mutual “deep, buried affection,” as Garfunkel put it, adding that the feeling was unburied at this year’s Grammy ceremony, where the two were awarded a Lifetime Achievement Award and opened the show with an acoustic rendition of “The Sound of Silence.”

The appearance then laid the foundation for this latest reunion tour.

“Because we do this every 10 or 12 years, this is probably the last time we’re going to do this,” said the perpetually mellow — and, it seemed on this occasion, slightly wistful — Simon, referring to getting together with his old friend.