The Pinkertons are mostly just rent-a-cops now, those beat guys skulking around warehouses at midnight, hustling winos out of fast-food joints, that kind of thing.

But then, the quality of your average criminal has declined too, as an exhibit of Pinkerton's memorabilia and 19th-century criminalia at the National Portrait Gallery illuminates in sad and telling detail.

Back in the good/bad old days -- Allan Pinkerton founded his celebrated detective agency in 1850 -- it was the age of the master criminal, safecracking wizards, cat burglars and international rogues. Criminals could be living legends, a status no doubt abetted by Allen Pinkerton's writing 18 books about his exploits in catching them, along with the myriad dime novels of the day celebrating the dark glamor of the James gang, or Butch Cassidy and the Sundance Kid, all of whom Pinkerton chased, but, as it happened, never caught.

Style! Check out the handbill that Pinkerton's National Detective Agency circulated on one Marion Hedgepeth, a Missouri train robber. (Imagine a criminal nowadays named "Marion Hedgepeth"!) He is described as "rather affable in manner; disposition cool, but at times somewhat reckless; dresses well but not flashily; has gold watch and chain, and may wear a diamond in shirt bosom."

Who wouldn't want to be described like that? After the Pinks, as they were known, nabbed the dashing Hedgepeth, hid jail cell was crowded with flowers from female admireres. And there he is on the Portrait Gallery wall, in the Pinkerton mug shot, staring with blithe frankness into the camera, under a derby with the front brim curled down just a rakish touch; a Chesterfield coat, a cravat, all this from a man who dynamited or otherwise rifled four railway express-car safes in his first year of brigandry.

"Both the cops and the robbers had more style back then," says Frederick Voss, a research historian, who along with his associate James Barber put this show together.

"There was more romance," Barber adds. "They took more pride in their work."

This was an age when we hadn't reduced humanity to nothing but a set of statistics, when we didn't pretend it was science curbing antisocial behavior, rather than cops collaring robbers. The human touch: The arkansas train robber Reuben Houston Barrows had "something of a lounging gait; when about town has hands in pockets in leisurely way . . . is something of a country storyteller, relating snake, dog and cat fights etc."

Can't you see that guy? And, sure enough, you can, in the photograph, with that hint of royal confusion in his face that marks a lot of this rogue's gallery.

It's largely photographs and memorabilia, with the exception of five paintings.

"We found that American painters didn't depict crime. It was more popular in Europe," says Voss.

Two of the paintings find their greatest glory in the fact that the pistol held by the robber in each one follows you around the room wherever you go, a Cyclopean Mona Lisa of crime.

Let's keep in mind here, in the midst of this romance, that the name of the Pinkertons got sullied by the decision of the company to hire out management goons in union disputes, the most famous event being a day-long gun battle between 300 Pinks and the workers at the Carnegie Iron Works in Homestead, Pa. Photographs and an engraving show the scene. i

"You go up around Schuylerville, Pennsylvania, you'll still find a lot of people who didnht like us," says George O'Neill, director of personnel for Pinkerton's Inc., and its unofficial archivist, down from New York to preview the show. Schuylerville, he says, is the area where the Molly Maguires, an Irish secret society, waged labor war on mine owners, until a Pinkerton named James McParlan, posing as an itenerant tramp named James McKenna, arrived to investigate their alleged crimes against the Pennsylvania and Reading Railroad. In 1876, after two years of buying drinks, McParlan had become a credible enough witness to help condemn 20 men to death for murder. It's a sad, Irish and alcoholic tale his meticulous and floridly penned expense account tells:

Treating O'Neill & friends at Fishers .70

Gallagher & friends at Sweeney's .80

Lost playing cards with MMs for drinks 1.20

An engraving which illustrated one of Allan Pinkerton's books shows McParlan being sworn in. An oil painting shows a chaotic trial scene.

The James gang, and a lot of their Missouri neighbors, hated the Pinkertons after a posse surrounded their house and an explosion blew an arm of Jesse's mother and killed his half-brother. The posse said the bomb was just an illumination device, and Mrs. James shouldn't have kicked it into the fireplace. The Pinkertons said they had no men with the posse. Legend has Jesse James and Allan Pinkerton stalking each other amongst the ferns of the lobby of the LaSalle Hotel in Chicago, but they never caught each other. The photograph shows Jesse looking to be a vengeful, calculating type, while his brother Frank has the look of a veteran bar fighter.

"I can't think of anybody we've killed," says O'Neill. With the exception of a long run of hangings, of course. One Bill Rudolph wrote a letter from jail in 1905 asking William Pinkerton, Allan's son and successor, to use his influence to get Rudolph's death penalty commuted, not just for himself, but for "a dear Old Mother's sake." Unfortunately, Rudolph had shot down a Pink, and he got no mercy from the agency.

The Confederate army got more respect. During a stint of intelligence gathering for the Union, the Pinks consistently overestimated enemy strength by as much as 100 percent, thus legitimizing the torpor of Gen. George McLellan, a charismatic do-nothing of the kind whose era ended the instant Lincoln located Ulysses Grant. Pinkerton is shown in photographs of time time, a dour little cigar-chomping guy with bulky brow ridges. He was probably 5-foot-5, says O'Neill, and he is dwarfed by Lincoln.

The terrible and wonderful glamor of 19th-century crime is best illustrated by the pictures of train robbers Butch Cassidy and the Sundance Kid, as in the movie of the same name, starring Paul Newman and Robert Redford. Butch and Sundance were not only handsome, they've got these terrific looks of sly delight on their faces, faces that invite you to cut the bull and go out and grab a little free money off those railroad trains, faces happy to plump the human soul to its most rapscallionish depths, the kind of faces that fathers habe been hating and daughters have been loving since the world began.

A Pinkertgon tracked Butch, Sundance and the lovely Etta Place (played by Katherine Ross in the movie) to Bolivia, where he found someone who said he'd seen them shot dead in the plaza of San Vicente. Other reports say they lived on, and it's hard not to be glad.

The Pinkertons have not only lived on but have prospered. It's a $285 million-a-year business now. Industrial security.Guarding offices. Dull stuff. A century from now, no curator at the National Portrait Gallery will be hanging a show about their 20th-century exploits. This show runs through Jan. 3.