Michael George Thevis, 46, this city's flamboyant millionaire pornographer who allegedly built an X-rated empire on extortion, murder and racketeering and who was one of the FBI's 10 most wanted men during his last seven months on the run, was captured yesterday when he walked into a Bloomfield, Conn, bank and tried to withdraw $31,000 from his checking account.

Thevis was serving 8 1/2 years for interstate transportation of obscene materials and conspiracy to commit arson when he escaped from a tiny Indiana county jail last April and dropped out of sight.

FBI and police had pressed the search for the fugitive with renewed vigor since gunmen ambushed Roger D. Underhill, 50, here just over two weeks ago. Underhill was the government's key witness in a 14-count racketeering indictment against Thevis, and had been expected to testify that the so-called Sultan of Smut had personally killed a peep-show competitor, stuffing his body in the trunk of a Cadillac.

Gunmen killed Underhill and Issac Galanti, a grocer whom the former Thevis aide was showing a real estate site, FBI informers had warned of contracts on the life of Underhill, who the FBI and the Justice Department had urged to enroll in the Federal withness protection program.

But the tough ex-con insisted he could take care of himself, carrying a 9mm pistol just in case. He never got to use it.

The death of the key witness has dealt a severe blow to the government's case against Thevis, and has had a chilling effect on other potential witnesses, according to one assistant U.S. attorney who is in charge of criminal prosecutions.

Until his capture yeaterday, Thevis seemed a phantom. The FBI had been unable to pick up a scent since the paunchy, balding Georgian walked out of the Indiana jail, just across the Ohio River from Louisville, where he was a defendant in a civil suit.

Just before he walked out of a door that had been disappeared, a Louisville jury had awarded several insurance companies and a peep-show competitor a $667,000 judgement against him in connection with the burning of a warehouse for which he was allegedly responsiable.

Witnesses said Thevis had ordered them to burn down the man's warehouse. Roger D. Underhill was one of the witnessess.

A former girlfriend, Patricia McClean, 28, has been charged with smuggling Thevis $6,000 that he used in the escape, but a U.S. District Court judge has granted a change of venue because of massive publicity generated in the wake of the Underhill killing.

McClean a former secretary whom Thevis had instateled as a $100,000 president of one of his companies reamins free on $250,000 bond. "She's a forlorn ex-girlfriend, abandoned and left to her own devices," says her attorney, Ed Garland.

When he fled, Thevis left behind an ex-wife and five children living in a $3 million Tudor-style mansion in north-west Atlanta, and a conglomerate of adult bookstores, X-rated theaters and legitimate business worth $100 million by his estimates. The operation was able to support the cadre of highpriced lawyers Thevis has required and still pay his ex-wife $30,000 a month.

Thevis was a maze of contradictions, a king of pornorgraphy at the office, a Puritan at home. He didn't allow so much as a Playboy around the house; he was afraid the children might see them, he once said.

He loved the power and money pornography made him, but he craved respectability. He used millions in an attempt to buy civic acceptance hereabouts. He was rebuffed.

Yesterday, Thevis was arrested with another woman, Jeanette Evans, an Atlanta realtor. She has been charged with harboring a fugitive. Both were reported transferred to Hartford, Conn, under strict security yesterday.

It was perhaps fitting that Thevis, who the government claims has built his coast-to-coast empire of titillation on murder, racketeering, extortion, arrested during a perfectly legal transaction. In fact, police, say the arrest was a fluke.

"We had no idea who we had at the time, but we knew it was somebody," said Bloomfield, Conn., Police Chief Harold Jackson, who had to ask reporters to explain exactly who Michael George Thevis was.

Thevis had shaved off his goatee, donned a toupee and adopted an alias.

The sequence of events that led to the capture began on Oct. 13, when he deposited a $30,000 check in an account at the Bloomfield State bank under the name of A.J. Evans, and a suspicious bookkeeper notified bank officials.

However, the check, which was drawn on the Citizens and Southern Bank of Summerville, S.C., cleared, and the money was deposited to the Evans account.

Still suspicious, bank President Joseph Gozzo called Bloomfield police, and agent Thomas Beatty dropped by the bank "to see if we could figure out what kind of transaction this was."

On Tuesday, Thevis phoned to say he would be dropping by the bank to withdraw $31,000 Curious police were waiting. Thevis told them he was a contractor from Meban, N.C. But officials there who knew the real Evans confronted Thevis on the telephone with personal questions about his fam.

A fingerprint check later verified Thevis' true identity, and FBI officials in Atlanta were notified. He had apparently been living in the Bloomfield area for a month or more, staying for the last five days at a motel in nearby Simsberry, Conn.

A late-model car driven by Thevis at the time of his arrest reportedly contained a number of valuables, including a large amount of cash and jewelry, according to preliminary reports.

When Thevis was confronted with his true identity, he told Bloomfield police, "Well, I knew it had to happen sooner or later. I knew they were after me."