Steve Martin dresses well. He's a sparkling conversationalist. But can he play "The Walker"? Paul Schrader thinks so. Schrader, who has written such film classics as "Taxi Driver" and "Raging Bull," has penned a new high society murder story. Its hero is one of those faithful male companions  known as "walkers" ;who escort rich women to parties that their busy and bored husbands want no part of.

"I've always been interested in lonely guys who drift around and peep into other people's lives, but never quite have a life of their own," Schrader tells us. Back in 1980, he wrote and directed "American Gigolo," in which Richard Gere starred as a high-class prostitute.

"The Walker," says Schrader, "is that type of character 25 years later, when his services are social rather than sexual. He's witty and he knows about art and antiques."

Like many real-life walkers, Schrader's is also gay: a successful real-estate broker with a younger Latin boyfriend.

Word was that Schrader was hoping to cast Kevin Spacey in the part.

"Kevin would be brilliant in anything," says Schrader. But, considering Spacey's discomfort with rumors that he actually is gay, Schrader never bothered to send him the script.

Instead, he pitched it to Martin. The comic actor C who, since his divorce from Victoria Tennant, has squired actress Anne Heche, artist Cindy Sherman and, lately, writer Ellen Ladowsky C hesitated at first. Says Schrader: "He just wondered, from an actor's point of view, how he'd do it."

Looking for "a prototype," Schrader suggested Martin "knock off" Gore Vidal. The best-selling author and onetime Senate candidate is hardly your typical walker. But, watching old TV interviews with him, Schrader and Martin liked Vidal's imperiousness and his family ties to Washington, D.C., where "The Walker" is set.

Schrader's story spins out of a fateful night when Martin escorts a senator's wife to a liaison with her boyfriend. When the boyfriend winds up dead, Martin provides her with an alibi. Then, the woman and her circle turn on him.

Schrader, who has also picked the brain of author Dominick Dunne for insights into the walker's world, says real-life socialites shouldn't fear a Capotesque expose. But his story has its parallels. The walker "ends up being like Susan McDougal," the Whitewater witness who went to jail rather than testify against the Clintons.

  Martin, who plans to give his character a Virginia drawl, tells us he's beguiled by "murder and noir" since starring in David Mamet's thriller, "The Spanish Prisoner," last year. "I'm psyched for this."