Where the Hirshhorn Museum and Sculpture Garden stands today, there used to be a horror show.

It was called the Armed Forces Medical Museum, and its exhibits were icky--an ulcerated colon, deformed human fetuses afloat in green formaldehyde, a shard of Lincoln's skull.

When James T. Demetrion first visited the site, he was a student teacher with a class of 11th-graders. He remembers vividly their squeals of disgust.

Things have changed a lot since then. The ulcerated colon has been sent to Walter Reed, other specimens-in-formaldehyde are up in Brooklyn raising Rudy Giuliani's hackles, and Jim Demetrion has put in 15 years as director of the Hirshhorn, which celebrates tonight that it's 25 years old.

Squeals of disgust are not uncommon these days in America's museums of new art. Imagine trying to run one. The business is a minefield. If you don't offend the artists, the dealers who promote them, the speculative collectors, the cautious, the voguish or the politically correct, there are always the politicians. That Demetrion, 69, has set off so few explosions is a testament to his surefootedness. Few stalwarts in the art world have attracted such goodwill, which ought to be apparent at "A Celebration of Art," tonight's $1,000-a-plate black-tie anniversary bash at the museum.

A Republican conservative, Sen. Bill Frist of Tennessee, and a liberal Democrat, Sen. Daniel Patrick Moynihan of New York, are two of the event's chairmen. The 69 artists who have signed up as co-sponsors have even less in common. They include international stars (Jasper Johns and Robert Rauschenberg), Washington painters (Sam Gilliam, Joe Shannon and W.C. Richardson), conceptualists (Bruce Nauman, Sol LeWitt), portraitists (Chuck Close, Cindy Sherman), classical abstractionists (Brice Marden, Ellsworth Kelly) and sharp-focus observers (Vija Celmins, Gregory Gillespie). Some are European (Gerhard Richter, Rachel Whiteread), and some are Californian (John Baldessari, William Wiley), and some are overrated (Matthew Barney, Julian Schnabel), some are underrated still (Louise Bourgeois, Richard Artschwager). That all of them together have lent their names to tonight's fund-raising dinner-dance says much about Demetrion's reputation for scrupulous fair-mindedness.

He doesn't look like a museum director. He's neither suave nor dapper. He used to be a high school social studies teacher in Ohio, and it shows. He doesn't have the plummy tones, the bespoke suits or the honeyed-moneyed background possessed by most in his profession. He's a janitor's son from Middletown, Ohio. He doesn't follow fads, or utterly reject them either. Part of his job in Washington, where the art market is dim, is to show us what is hot in London and Manhattan.

"I don't hate the art establishment, I really don't," Demetrion insists. "I like a lot of that stuff. I really do."

But to see what art he really loves you have to look at his collecting. Demetrion's museum has dutifully displayed many blown-up photographs--in the '80s and the '90s there was no way to avoid them--but has collected almost none. Nor has it purchased names. Ask anyone in the field. Demetrion is known for focusing his buying on specific works of art with what Neal Benezra, his assistant director, calls "obsessive attention to clarity of expression."

More than 12,000 objects of every description were given to the museum by its founder, Joseph H. Hirshhorn (1899-1981), an immigrant wheeler-dealer raised in abject poverty (the 12th of 13 children, he quit school at 14) who bought art with the hunger of a boy who'd never had enough toys. Abram "Al" Lerner, the Hirshhorn's first director, made that collection into a national museum. Demetrion has been pruning it ever since.

Some museums aren't allowed to sell their benefactors' gifts, but considerate Joe Hirshhorn, whose collection was immense, and heavily New Yorkish, imposed no such restrictions. Demetrion, accordingly--and with his board's permission--has sold off scores of objects, always using all the proceeds to buy choice works of art.

"We may be the only modern museum in the world," he says, "whose collection has decreased."

When many other modern-art museums were paying most attention to the more austere abstractions or the jauntiness of pop art, Demetrion instead was focusing his thought, and his exhibition schedule, on one sort of European figurative art.

In 1987 the Hirshhorn showed Lucian Freud's retrospective. No other American museum was willing to display that patient Englishman's fiercely candid portraits and ruthlessly naked nudes. The next year Demetrion displayed the gnawed-at figures of Alberto Giacometti; in 1990, Ilya Kabakov; in 1993, Jean Dubuffet; in 1996, Richard Lindner; in 1997, Stanley Spencer, that passionate, God-struck Englishman. These tough shows, viewed together, detail a chapter of European art that few other institutions have done more than sketch.

Demetrion never planned on becoming a museum director. He earned a BA (his only degree) in education, from Miami University (Ohio) in 1964, and then got drafted. In Munich he saw a wall of Rubenses ("the enormous bodies, the confined space"), and something clicked. In California, after his military service, Demetrion took a survey course in art at San Jose State, and saw how much he loved it. "I had the audacity," he remembers, "to teach an art course to adults, at night, in a local junior college. I was just two pages ahead of the students, but by then I was hooked."

Between 1958 and 1962, he worked toward a doctorate at UCLA, which he never got. But he met some real artists, Richard Diebenkorn, for instance, and watched them at their work (at the Tamarind Lithography Workshop), and spent a year in Vienna studying the tortured figures of Egon Schiele. Then he met Walter Hopps.

Hopps is a former director of both the old Washington Gallery of Modern Art and the Corcoran Gallery; at one time, he was the most important art scout in this city. He had the best connections, the broadest mind, the sharpest eye. Hopps was the director of the Pasadena Art Museum when, in 1964, he hired Demetrion as his curator. But then Hopps left, and Demetrion took his job. He spent three years as director there. After that he spent 15 years in Iowa, directing the Des Moines Art Center, where the rightness of his judgments, and the skill of his collecting, earned that institution a national reputation. Then the Hirshhorn called.

Demetrion and Hopps had this at least in common. When you thought you'd figured out what they would show you next, they utterly surprised you. Though Demetrion has shown lots of angst-gnawed pictures, he has also organized an exhibition of the transcendentally calm still lifes of Giorgio Morandi.

For his next exhibit, Demetrion is organizing a retrospective of the anguished abstractions of Clyfford Still that will open in 2001.

The Hirshhorn is a serious institution. It doesn't shock just to merely shock, or soothe to merely soothe.

And it doesn't throw a lot of fancy fund-raisers either. Black-tie parties, a dime a dozen at most Washington museums, are rare as hens' teeth at Demetrion's Hirshhorn. He is known to rather hate them. This one (the Smithsonian these days is urging its museums to get out there and raise money) is the first in recent memory. And it raises a question: Will Demetrion, long known for his resistance to such fanciness and folderol, show up in a tux?

CAPTION: James Demetrion, on view tonight at the Hirshhorn's 25th-anniversary fund-raiser.

CAPTION: James Demetrion, left, Neal Benezra and a Warhol self-portrait.