A story in yesterday's editions of The Washington Post incorrectly identified the federal department that had employed William Sibert, 30, who was convicted of embezzling $857,557 from the U.S. government. Sibert had been a GS-5 financial assistant in the Urban Mass Transit Administration of the U.S Transportation Department.

William Sibert, 30, had been looking over his shoulder for several weeks. And on Aug. 5 as he checked his baggage for a flight to Chicago from National Airport he thought he saw several neatly dressed men watching him closely.

At O'Hare airport as he was getting his flight to Las Vegas, Nev., he realized there were too many men wearing TWA jackets for a routine flight. Later, during the flight, he told his seven guests in the first class section to order final round of drinks. The caper was up.

William Sibert, a pudgy, GC-5 Treasury Department employee, walked off the plane into the arms of federal agents who confiscated $59,000 he had embezzled from the government. Then they canceled his reservations for plush suites at Caesar's Palace, and left his friends to pay their way home.

Thus ended the brief but spectacular Walter Mitty adventure of William Sibert. He had spent most of the $857,557 he embezzled from the Treasury Department in what was probably the largest spending spree ever by a civil servant whose $10,000 annual salary could not cover bills for his wife, infant son and himself.

Yesterday, Sibert was sentenced to serve six years in jail - a sentence he will have to serve after doing six months on an unrelated gun charge. Last week, in an interview in jail, Silbert describe his adventure and how it began one night last spring when he was working overtime as a financial assistant in the Urban Mass Transportation Administration.

Sibert, who was in a position to release grant funds for subways, had long felt he could transfer funds to himself and that it would slip by his boss. That night, beset by bills, he made a voucher ordering payment of $55,916.47 to William Sibert. A supervisor signed it.

Sibert then ordered his home mail delivery stopped for several days so he could pick up the check at the post office without his wife's knowledge. Even after he got the check, he held on to it for several days and thought about turning himself in.

"Then I thought, 'Heck, if you're going to get caught doing it, do it right," Sibert said last week."If you're going to go on something like that, there's only one way - all out."

That he did. In slightly more than two months, he issued vouchers for nearly $900,000. He also grew a moustache, got tinted glasses, a new hairstyle and more and better double knit leisure suits.

Telling acquaintances alternately that he had won his new found wealth gambling or had won a massive insurance settlement, he spent nearly $200,000 on at least 12 cars for friends and members of his family and took coworkers to lunches on the southwest waterfront where he would pick up $500 tabs. He also bought a new $60,000 house with a swimming pool and renovated it for $30,000, outfitting it with $10,000 worth of such items as closed circuit TV systems and pink and white shag carpeteting.

In addition, he said he bought a 30 foot houseboat, made gifts of $8,000 or so to women who worked in his office - trinkets such as diamonds rings IBM and ITT stock purchased through his account at Merrill-lynch - and paid $80,000 for a topless bar a block from FBI headquarters.

In the process, he discovered banks would give him tens of thousands of dollars in cash for U.S. Treasury Department checks - no questions asked. He said he opened an account at the Suburban Trust Co. branch in Suitland for $50, and withdrew $21,000 the same day. His cash flow ultimately became so fishy that the bank alerted the Treasury Department.

"It really surprised me that the bank would handle that kind of money," Sibert said, "but they told me Treasury checks were good on the spot."

One day, Sibert claimed, the bank was forced to close its doors for several hours and wait for another money delivery after Sibert withdrew $36,000 early in the morning.

Also as he spent his money, Sibert said he experienced what might be the ultimate in impulse auto buying. He had become a regular customer at Wilson-Powell Lincoln Mercury in Marlow Heights, a dealership upon which he heaps praise for their handling of numerous automobile deals for him and their "terrific service."

When Sibert talked about his cars - luxury cars of all styles - he spoke with more emotion than about any other of his other purchases or high priced travels.

"Those are two beautiful cars," he said fondly of two customized Continental convertibles he purchased. He described all 12 automobetes he bought for various members of his family and a female friend's family. He ticked the cars off one-by-one, Mercedes by Lincoln by Datsun 280-Z, and remarked, "Twelve? That's about right. I've always had a thing about cars.

He said he tried to tell his sister at one point that a Mercedes was "a bit too much" for her, that he wanted to buy her a smaller car and give her money for a house down payment instead. But gave in to her wishes. If someone could not make a decision about the type of car they wanted, he said, he would just choose for them.

And there was the day when he finally gave in to temptation to buy a $27,000 car in the Wilson Powell showroom for himself. He was there to have some of his cars serviced, he said, when he thought to himself, "Damm, I just might as well go ahead and get that thing" and wrote a check on the spot.

Ironically, Sibert's six year sentence for the $857,000 theft is not the longest he has received. He was sentenced to eight years - of which, he served six for his guilty plea to a Maryland housebreaking in which no property was taken shortly after he finished high school.

Sibert, who said he would do the same thing under the same circumstances again - while at the same time explaining that doesn't mean he'll do it again when he gets out of jail - said he doesn't have the slightest bit of sympathy for the government.

"I don't feel like I've done a crime against the government," Sibert said. "I don't think it's a living thing. The government's screwed so many people in so many ways that I don't feel I've hurt my government. The government is not something that has a feeling."

Instead, he said, the bureaucracy was inept when it put so much trust in him - a convict - sloppy in its handling of billions of dollars and "stupid" in the way it has attempted to recover property he bought with the stolen funds.

He said he was surpirsed it took the government nearly four months to work out a $900,000-plus civil judgement against him and to get deeds and titles to his property. He also said he had consulted an attorney to make sure that persons to whom he gave gifts could not be forced to give them back if he was arrested. But he added that most of the people were "scared" by government agents into returning the gifts.

One of his hopes, he said, was that his wife whom he was leaving at the time would be well fixed when he got caught. However, she has returned all of the property and was herself briefly arrested before convincing the government she was not part of Silbert's scheme.

A female acquaintance, Lois A. Benson, was arrested with Sibert in Las Vegas and also was briefly charged. She has since signed an agreement returning to the government nearly $60,000 worth of gifts and cash.

Sibert's notoriety cuts both ways in his current prison atmosphere, he said. The inmates "think it's cool" that he stole so much money, he said, but some guards "are jealous." He said he is also afraid that the publicity will result in his spending "too much time" in prison, considering the amount of property the government has recovered.

He also knows he could have committed his crime in a more complicated way, and escaped detection longer, he said. But, he added, "It's a heck of a strain to know somebody's going to tap you on the shoulder sooner or later."

This way, he said, he must have known it would be sooner. "Issuing a check in my own name, instead of using a dummy corporation to hide the assets, was the stupidest thing I'd ever done. But I did it out of desperation of the money. I wish I'd never done it."