It is one of a kind, a massive, thriving oddity in a land where travel has come to mean flight. Grand Central Terminal is a city within the city of New York, where you can get dark-needled sea urchins to go; all the chocolate chip cookies your digestive system can stand; fat, red, heat-seared bockwurst, giant pretzels, bagels, oysters, Alka-Seltzer.

You can get your shoes shined, play a quick game of hand ball, cash a check, copy a re'sume', bet on a horse, buy a book, flowers, coffee beans, a blow-up of Mount St. Helen's. You can catch the subway or any of the 551 trains departing daily. You can also, if you're not careful, lose a necklace, a purse, a wallet, a suitcase.

The depot has its own police force, its own emergency clinic, its own clockkeeper nicknamed "Tick Tock." It has more than five miles of passageways, 85 retail shops.

Half a million people scurry through Grand Central every day, pouring like a human waterfall down steep escalators from the Pan Am Building into the main concourse, snacking at restaurants, cutting through to Park Avenue or any of the thoroughfares that jut from the terminal.

Grand Central has been called the greatest of the world's rail terminals, although at 69, its age is showing. Its name is an American cliche'. It is not a station, it is a terminal, those attached to it heatedly point out. Trains pass through stations. Their runs begin and end at terminals.

There was a time when the terminal never closed, when travelers marched its Tennessee marble floors to catch the Twentieth Century Limited, the Yankee Clipper, the Wolverine, trains that would take them to New England or Chicago, and from there, as far as the Pacific. The big year was 1946, when Grand Central accommodated 63 million people.

You can still catch a train to Montreal or Toronto or Poughkeepsie, but Amtrak schedules only 24 long-distance trains a day now. Conrail operates three commuter lines for the Metropolitan Transit Authority, with 527 runs in and out of the terminal. The farthest is to Dover Plains, N.Y., 76 miles away on the Harlem line. And there is the endless screech of the subway.

Grand Central occupies 48 acres in midtown Manhattan, some of the choicest real estate in the world, the sort of property that makes developers salivate. According to the MTA, some of the 110 firms leasing space in the terminal pay $296 a square foot. The MTA, which leases the terminal from Penn Central, the owner, gets $3 million to $4 million a year in rental fees.

But while developers twist their hands wistfully, the city has taken steps to assure that Grand Central will be with us awhile longer. The terminal was declared a landmark, and when that designation was contested, the fight went all the way to the Supreme Court, where the landmark status was upheld.

Nonetheless there is a odd marriage of styles where the terminal bunches together with its neighbors. The Pan Am Building, which Conrail's Tim Connor says has a daytime population rivaling that of Peoria, Ill., is 59 stories high. Like the terminal, it straddles Park Avenue, a sleek skyscraper with a red Pan Am sign that mugs in photos of Grand Central taken from Park Avenue.

Grand Central has been called a magnificent sample of the Beaux Arts style and, less kindly, "Mussolini modern."

It was built in 1913, to replace a glass and iron predecessor that collapsed under the weight of heavy snow. The New York Central converted its steam trains to electric, remained in midtown Manhattan, and stimulated its development. In its main concourse, 275 feet long and 120 feet wide, thousands of people jammed together on Feb. 20, 1962 to watch on a giant screen the lift off of Col. John Glenn Jr., in America's first orbital space flight.

On New Year's Eve, 1963, the concourse became a charity ballroom, and Guy Lombardo played, but Station Master William J. Haley, who started as a mail loader 41 years ago, recalls that it was goosebump weather; a lot of guests were too chilly to dance.

A couple of elephants were unloaded at the terminal once and had trouble finding a suitable exit. They used a taxi ramp. And back in the '50s, 35 Los Angeles policemen in town for an American Legion convention screeched out of a baggage car on motorcycles, and scattered crowds in the main concourse on their way to an exit ramp.

There's rhythm to a day at Grand Central. It wakes up about 5:30, the official opening time, and within the hour the smell of freshly brewed coffee wafts through the station, as restaurateurs prepare for the onslaught and the achievers who left home too early or too eager to stop for breakfast.

At 7 o'clock the commuters are tackling elevators and exits, scrambling to their midtown offices. The crush of traffic lasts about two hours. Things settle down a bit. There are munchers, strollers, admirers of the backwards zodiac painted in blue on the 125-foot high concourse ceiling.

Three o'clock is the beginning of crime time. According to John V. Esposito, superintendent of railroad police in the Metro region, more crimes are reported from 3 to 11 p.m. than during other hours. Last year, the 108 members of his force arrested 1,853 people. The conviction rate, he said, was 87 percent.

"We got a lot of eyewitnesses in a place like this. Also, we do a lot of investigation before we charge 'em."

Some 194 of the arrests were for felonies, including one homicide. There have been no murders so far this year.

A Jesse James-style train robbery was carried out en route to White Plains, Esposito said, and within 24 hours the four suspects were identified. Twelve hours after that, they were arrested. Now they are all in jail.

There are countless "switches"--a man offers to help a woman carry her suitcase to a locker, installs it, hands her a key. Only he has palmed the real key, and when she returns to the locker, her possessions are gone.

The railroad police also handle rape cases, suicides, lost children, runaways, drug cases, bomb threats. There's a "bomb dog" trained to sniff out explosives, a German shepherd named Darth Vader, also known as Irving.

The second great mass movement of humanity occurs, predictably, from 4-6 p.m. The station closes at 1:30 a.m. In winter, a few of New York's 30,000 "bag ladies" escape the frigid nights in corners of Grand Central. Esposito recalls a celebrated attempt by Mayor Ed Koch to persuade a "bag lady" to get into his car and go to a hospital "for treatment." Summoning all her indignation, the woman refused, and called police.

The mayor, in turn, refused to take "no" for an answer, and telephoned through officialdom until he found an authority to commit the woman. He returned to Grand Central, Esposito said, with local TV cameras rolling, and the woman was finally hauled off, sputtering her protest. But she got the last laugh. The hospital examined her, refused to commit her without a second signature, and, the chief said, she was back at Grand Central the next day.

People do rest against the terminal and nearby shops on sidewalks outside, but railroad police discourage loitering inside. In the chandeliered waiting room, wooden pews are filled with those who don't appear to be between trains, and uniformed officers patrol and occasionally have words with them.

Recently, there have been reports of "street people" living in steam tunnels below the station and elsewhere in subterranean city channels. But station master Haley says the reports are not true. There are tunnels that one could walk from 41st clear up to 50th Street north of the Waldorf Hotel, but Haley and the Conrail people discourage visitors, and those who do enter the tunnels are advised to be accompanied by police.

Haley is contemplating retirement, and he acknowledges that his 41 years at Grand Central have brought a few surprises. He recalls a couple of packages left in Lost and Found that contained not merchandise, but snakes. There was also a wooden leg left aboard a train. Its owner was tracked down.

Presidents and other stars have passed through, but Haley is blase'. "I'm not a hero worshiper. I've seen 'em right from Roosevelt on. I've never paid much attention to any of 'em."

Despite this, he opens a drawer and pulls out a key. Franklin Roosevelt had his own rail car, which was parked underneath the Waldorf. A private rail line leads to the hotel from the terminal.

"They used to lower him onto the platform and into the freight elevator," since the president was unable to climb stairs. Haley held the elevator key used in that presidential operation.

Some who work at Grand Central develop a kind of chauvinism about the place. Haley calls it "the cathedral of transportation." To Esposito it is "the jewel of the city."

Just beyond the jewel, and the colorful people resting against its exterior or streaming past its 13-foot wall clock where Minerva, Hercules and Mercury have been lounging for 69 years, the Grand Central visitor can catch a glimpse of the Ninth Street Stompers.

Musicians are not allowed in the terminal, but occasional trumpet notes make their way through a portal as the straggling of musical artists in slicked down hair and Bowery coats hit the high notes, grin at each other and look meaningfully at their money hat.

They seem a bit leftover from more prosperous times, and passers-by, surprised at the gleeful tour de force, often oblige them with coins and the coveted dollar bill. Music for dancing, the musicians say.

Last of the big-time terminals, last of the big-time bands.