Former U.S. Park Policeman Paul Dwain Shepherd was sentenced yesterday to 15 years in prison in a plot to kidnap J. Willard Marriott for ransom last August.

In sentencing Shepherd to serve three consecutive five-year terms and a fourth concurrent with the others, U.S. District Judge J. Calvitt Clarke Jr. declared: "I know that sentencing you to a prison term is going to wreak hardship on your family, but that's not the law's fault. That's your fault."

Shepherd got the maximum penalty for traveling in interstate commerce to promote kidnapping and extortion and two counts of soliciting for the commission of a felony. The maximum for the fourth offense, attempted abduction with intent to extort money, is 10 years imprisonment.

Clarke, sitting in Alexandria, denied a motion by Shepherd's attorney, John Keats, to allow the former policeman to remain free until his appeal is heard by the U.S. Fourth Circuit Court of Appeals.

"There is substantial chance the defendant may flee the community." Clarke said, Shepherd, a diabetic, allegedly tried to kill himself last Nov. 30 by taking an overdose of insulin two days before his earlier scheduled sentencing date.

Shepherd, 44, was accused along with his brother, Billy Ray Shepherd, 52, of attempting to kidnap the hotel and restaurant magnate or Mrs. Marriott last August in a plot to extort $500,000.

Billy Shepherd, a Calvert County, Md., school maintenance employee, pleaded guilty midway through the trial to one count of conspiracy to use a telephone in interstate commerce to extort money. He was given a five-year suspended sentence plus five years of probation.

During four days of testimony the policeman's attorneys argued that he was lured into a plot concocted by FBI agents.

Prosecutors said Shepherd was "tired of being a poor cop," and wanted to retire in two or three years with $600,000 in the bank. Shepherd had planned to commit two other kidnaping after the Marriotts', according to witnesses.

Keats noted in his statement to Clarke that a probation report said Shepherd "didn't progress as well as he should have as a park policeman."

The kidnap plot "was a fantasy," Keats said. "I think he probably articulated [the fantasy] to the wrong person. Mr. Shepherd really had no firm plan. This is a man who tried to abide by the law all his life.

But U.S. Attroney Justin W. Williams said the plot was "not a fantasy, but a reality with dreadful potential consequences."

Shepherd did not speak in his behalf yesterday.

Clarke said he had received numerous letters on Shpeherd's behalf which he found "appealing." But he said he had a "different interpretation of the evidence" than Shepherd.

"You knew Mr.Marriott was in frail health," Clarke said to Shepherd."You made statements about what yuo'd do Mrs. Marriott."

According to testimony Shepherd said if Mrs. Marriott caused any problems he would not hesitate to "snap her head off" and let her bleed to death.

"Kidnapping is one of the cruelist crimes . . . because of the mental grief to others," Clarke said.

Shepherd will be eligible for parole in five years.