BALTIMORE, NOV. 8 -- Silver Spring accountant Joel D. Davis was sentenced in federal court today to 15 years in prison for conspiring to murder an Internal Revenue Service agent who was auditing his books.

As friends and supporters in a packed courtroom gasped and wept, Davis was ordered imprisoned for an additional three years for masterminding an insurance scam in 1980 to burn down a vacation resort he owned in New York.

The man he hired to set the fire had testified that Davis told him to scrawl antisemitic graffiti on the walls of buildings at the Torahtowne summer resort to deflect suspicion from Davis. There was also testimony at Davis's trial last spring that he paid arsonists to burn down the old Yeshiva High School on Kemp Mill Road in Wheaton in 1977.

As U.S. District Judge Walter E. Black Jr. imposed the combined 18-year sentence, Davis's shoulders slumped, but he showed no other emotion.

Black called the murder scheme a "matter of great severity" that justified a heavy penalty. The maximum sentence for conspiring to murder a federal agent is life imprisonment, a sentence rarely imposed. Prosecutors said Davis will be eligible for parole in nine to 12 years.

"I am terribly sorry for what I did and for the harm I caused to others," said Davis in a statement read by his attorney, Joshua R. Treem. "Somewhere I stumbled, and I deeply regret those actions."

Davis, 48, was ordered to report to prison Jan. 7. Black permitted him to remain free on a $250,000 bond secured by property belonging to Davis family members. Davis, who has dual U.S.-Israeli citizenship, surrendered his passports several months ago.

Today's sentencing brings to an end a decade-long saga of intrigue and legal maneuvering in which Davis was implicated in both the arson and murder schemes before he moved to Israel in 1982.

There, he lived with his family, set up a retail ice cream business and became an Israeli citizen before being arrested in 1987. He fought extradition but was returned to the United States in October 1989.

According to prosecutors Gregg L. Bernstein and Peter M. Semel, Davis hired the same three men for both the murder scheme and the arson.

One of them, convicted felon Douglas L. Sanders, 51, was paid $20,000 by Davis to kill IRS agent W. Stewart Connard, who was auditing Davis's tax returns in 1980, according to Bernstein and Semel.

The agent, they said, had discovered irregularites in several tax-shelter partnerships Davis had set up for himself and relatives. Sanders hired two confederates, Robert Lee Smithson and Johnny Zarou, to carry out the killing, the prosecutors said, but before it could be done, Smithson was arrested by Montgomery County police on an unrelated charge and began confessing to the murder plot.

Sanders was arrested and convicted in 1982. Davis moved to Israel just before Sanders's trial.

Once brought back to the United States, he pleaded guilty in the plot. He also was convicted of arson-related racketeering in hiring Sanders to burn down the resort 50 miles north of New York City to collect $168,000 in insurance on the property.

Bernstein contended at today's sentencing that Davis fled to Israel at least in part to avoid prosecution. Treem said Davis moved when he "perhaps realized that he could not reconcile what he had done with his moral and religious upbringing."

Treem characterized Davis as a religious man deeply involved in charitable and eductional work in the Jewish community. But prosecutor Bernstein said he used the checking accounts of such organizations "for his own personal expenses" and even paid Sanders from the accounts.

Now destitute, according to Treem, Davis also is a target of the IRS, which says he owes nearly $1 million in back taxes and penalties.