"Tell me something, do I look as absurd as I think I do?" asked Herb Schmertz, the PR whiz of Mobil Oil, Tuesday night at Bloomingdale's.

The record will speak for itself, but Schmertz was sporting his cowboy outfit, complete with the monstrous black hat he claimed to have worn on a plane back from Phoenix on a dare five years ago.

But he was not alone. Several hundred paunchy, middle-aged executives, accompanied by similarly attired women, stuffed themselves into designer jeans, $40 Western shirts, chamois vests, Neiman-Marcus cowboy hats and rococo cowboy boots to raise money for the National Committee, Arts for the Handicapped, a pet project of the Kennedy family.

In a word, the New York cowboy had arrived.

The Western attire was in keeping with a new event on our calendars, the Ralph Lauren week, in which the ubiquitous New York designer features his new line of Western clothes for men and women.

There is a world of difference, though, when his clothes are on his lanky male models with flat stomachs as opposed to the leaders of the corporate world, who pack some middle-aged spread.

But no matter. The evening was a great success from everyone's point of view: The Kennedys raised a lot of money for the Handicapped; Ralph Lauren, Loomingdale's and the Lone Star Cafe got great exposure, and everyone made a good-natured fool of himself.

Lauren, in fact, got more than exposure Tuesday night. The cash register in his new shop kept ringing as guests succumbed to his Western fashions. Eunice Kennedy Shriver and Pat Kennedy Lawford left the benefit wearing spanking new cowboy hats.

Some paid only minimal homage to the Old West, though. Arthur Schlesinger, for example, showed up in a tweed sport coat and shirt, under which appeared to be a yellow item somewhere between an ascot and a neckerchief.

"I exploited the full resources of my wardrobe, and this is what I came up with," he explained.

And Adolph Green, who is a regular at such New York events, wore what looked suspiciously like a tired fedora.

As at any bona fide Kennedy affair, a number of stalwarts who trace their roots back to the New Frontier and beyong made appearances. Schlesinger (who roomed with John Kennedy at Harvard) and his wife, Lemoyne Billings, and Stephen Smith and his wife, the former Jean Kennedy, who is national chairperson of the Very Special Arts Festival, all showed up. They were joined by Kennedy sisters Eunice Shriver and Pat Lawford; sister-in-law Ethel Kennedy, accompanied by tennis promoter Gene Scott, and a gaggle of younger Kennedys.

In addition, appearing in indescribable variations on the Western theme, were Norman Mailer and companion Norris Church; the ever-etiolated Andy Warhol; Tammy Grimes; Jamie Wyeth and his wife, Phyllis; Geraldine Fitzgerald, Tom Brokaw and his wife, Meredith; Green, and Margaux Hemingway.

The Lone Star Cafe, a current winner in the mercurial world of New York watering holes, provided chili, ribs and liquor, and lent its own Fifth Avenue brand of Country-Western atmosphere and music to the evening.

Two groups of handicapped youngsters from Newton, Mass., and Jamaica, N.Y., sang and danced for the audience of about 500 after dinner. Country-Western singer Eddie Rabbitt flew in from Las Vegas to sing briefly, and the, perhaps in a sign of things to come, square dancing-not disco-reigned later in the evening.

From the beginning, this was to be no ordinary benefit. Jean and Stephen Smith originally were to pull up to the Third Avenue entrance of Bloomingdale's in a stagecoach, which looms as a serious alternative these days to the hazardous New York subways. The plan did not work out, however, and they arrived like most of the other 20th-century cowboys: in a limousine.

Brokaw, who arrived with the Smiths, claimed to have had his outfit for years.

"I'm from South Dakota," he said, apparently explaining everything. He conceded later, though, that he rarely had been on a horse. "But I've worn the boots on the air a lot," he added.

The benefit was in conjunction with the National Very Special Arts Festival in Washington later this week, sponsored by the National Committee, Arts for the Handicapped.

With an initial grant from the Joseph P. Kennedy Foundation, Jean Smith founded the committee four years ago to promote the artistic talent of handicapped young people, and has exploited her connections wisely to enlarge it since then. Forty-seven states now participate in the program, and about 1.5 million people are involved.

She rejects the notion that Americans will balk at the millions of dollars of expenditures that go with wider recognition of the needs of the handicapped as quickly as her brother rejects a similar fiscal argument against his national health insurance program.

"You just can't do that with these kids," she said.

Meanwhile, the band played on, the chili dwindled and everybody forgot how silly they looked. The New York cowboys and cowgirls were having a good time. CAPTION: Picture 1, Ethel Kennedy, Tom Hane, Tom Brokaw; photos by Donal F. Holway.; Picture 2, Kerry Kennedy, left, Andy Warhol, background, and David Maleska.