A U.S. park policeman and his brother, who allegedly conspired to kidnap restaurant and hotel-chain magnate J. Willard Marriott or his wife with the help of an accomplice who actually was an FBI agent, were arrested yesterday after a fake kidnapping was staged.

The policeman, Paul Dwain Shepherd, 44, of White Plains, Md., allegedly told te FBI agent that within the next two years he planned three of prominent Washington figures, including the Marriotts, because he was "tired of being a poor cop" and wanted to retire in two years with $600,000 in the bank, according to an FBI affidavit. The affidavit alleged that the Shepherds planned to ask for $600,000 in ransom money in the Marriott kidnaping.

Shepherd was arrested at his office at D.C. Superior Court after the agent, who was not named, called him and said he had kidnaped Marriott according to plan, the FBI reported. Sheppherd was held in lieu of $50,000 bond in the D.C. jail.

Shepherd's brother Billy R. Shepherd, 52, of Owings, Md., a custodian for the Calvert Country school system, was to be the look-out during the kidnaping and ransom pick-up the affidavit alleged. He was arrested in Maryland and is being held in lieu of $250,000 bond in the Baltimore jail.

Colleagues of the younger Shepherd, a park policeman for 14 years, said there were shocked at his arrest. Shepherd, who was paid $18,000 a year, was described as "very personable, a very congenial and personable chap," by Park Police spokesman George Berlacy. Shepherd volunteered last Christmas to play Santa Claus at the Pageant of Peace ceremonies on the Ellipse, Berklacy said. Shepherd stood next to President Gerald Ford and distributed treats to children.

The FBI became aware of Paul Shepherd's alleged plot two weeks ago through an informant, according to U.S. Attorney William B. Cummings in Alexandria.FBI sources said the Marriotts were informed of the kidnap plot and played along.

Last Wednesday the undercover agent posing as a co-conspirator contacted Shepherd by phone and set up a meeting for 7:30 that night at Washington National Airport in front of the American Airlines ticket counter, according to the affidavit filed in the U.S. magistrate's office in Alexandria.

Shepherd allegedly told the agent he planned to kidnap either Marriott, 76, or his wife Alice Sheets Marriott, 69, for the $500,000 ransom.

Shepherd told the agent he had been to the Marriott residence on Garfield Street in Northwest Washington on three occasions as part of his job and that he thought of the kidnap plot the last time he was there. Because the Marriotts are so wealthy Shepherd allegedly told the agent the money would be paid without any notification of police, according to the affidavit.

Shepherd may have met Marriott by escorting him to the Marriott Corp.'s "Music 76" program last year on the Washington Monument grounds, Berklacy said.

According to the affidavit, about 15 minutes after the airport meeting, Shepherd, riding in the agent's 1977 Pontiac, directed the agent north on the George Washington Memorial Parkway and across Key Bridge to the Marriotts' house on Garfield.

Shepherd then allegedly told the agent to drive about five or six blocks from the house to a spot where Shepherd said Marriott should be switched to another vehicle after the abduction.

Shepherd told the agent he initially planned the operation with his brother, but that Billy did not have the nerve to go into the house and do the actual kidnapping, the affidavit alleged.

Marriott was to be held at the Falls Church home of Shepherd's girl friend who also works at Superior Court, the affidavit said. His girl friend would be out of town and did not know about the plot. Shepherd allegedly told the undercover agent.

Shepherd said that at 10 a.m. yesterday, the time agreed on for the abduction, he would be at Superior Court where he acts as a liaison officer between the Park Police and the court system. The agent was to call him after the abduction and Shepherd would then phone Marriott's son, J. Willard Marriott Jr., and ask for the ransom, the affidavit alleged.

Shepherd told the agent he would take out his false teeth and put gum in his mouth when he made the call so that a voice print comparison could not be made by police, according to the affidavit.

Marriott's chauffeur was supposed to take the ransom money to the Hertz Car rental office at National Airport and also pick up a rental car, according to the alleged plot. The chauffeur would then be ordered to drive the rental car to several undisclosed check points and before reaching the ransom drop-off point, Billy Shepherd was to disable the car he was driving to prevent other vehicles from following the chauffeur, the affidavit alleged.

To prove his sincerity about the plan, Shepherd last Friday gave the agent his Smith and Wesson service revolver, his U.S. Park Police identification card with photo, a Park Police uniform and a personal check for $24,000, the affidavit alleged.

In accordance with the plan, two FBI agents yesterday masqueraded as Marriott employees in company uniforms and drove in a company van to the Marriotts' home at 9 a.m. They took a "body bag" into the house and once inside, they stuffed it with blankets and pillows to make it look like Marriott's body, FBI sources said.

They then brought the bag back out to the truck and put it in the back in case Shepherd had someone watching the house, the sources said.

Once the hoax was completed, the agent called park policemen Shepherd at his office, the sources said. About 10 minutes later Shepherd, who was under surveillance by FBI agents at the courthouse, left his office and walked the two blocks to the Hecht Co. store where he allegedly called the younger Marriott from a pay telephone. Shepherd told Marriott that his father had been kidnaped and that he should go to his father's home and await another phone call at noon, the sources said.

The son, who was expecting the call , "did a superb acting job," an FBI source said.

Shepherd told the undercover agent at one of several meetings that he was "dedicated to the idea" of the kidnaping and appeared so obsessed with the plan that he would kidnap Marriott with or without the agent's help, the affidavit alleged. A videotape was made last Thursday discussing the kidnap plans, according to the affidavit.

After his arrest yesterday, Shepherd was deemed to be absent without leave, Berklacy said. Today his status will be changed to administration leave without pay, Berklacy said.

Shepherd, a native of Bartley, W. Va., had a good service record with the Park Police and an "excellent relationship with other members of the force and the public," Berklacy said. Several colleagues reportedly cried when they heard about Shepherd's arrest because he was so well liked, they said.

Shepherd was a graduate of Garden High School in Oakwood, Va. He served in the U.S. Army from 1953 to 1955 and was honorably discharged.

From 1955 to 1961 Shepherd worked with the Armco Steel Corp. in Baltimore and from 1961 to 1963 he was a maintenance employee with the parks and forestry department in Maryland.

Billy Shepherd has been a laborer for the Calvert County schools for about a year, according to a school spokesman. He reportedly earns about $8,000 a year. Shepherd's employment status is under review pending the outcome of the charges, the spokesman said.

During a bond hearing yesterday in U.S. Magistrate's Court in the District, U.S. Attorney E. Lawrence Barcella Jr. characterised Paul Shepherd as a "cold, calculated desperate individual who would chuck a whole career for big money."

Barcella argued that Shepherd should be placed under $250,000 bond. U.S. Magistrate Henry H. Kennedy Jr. said the severity of the alleged crime showed a man "in desperate straits." He then set bond at $50,000. U.S. Magistrate Paul Rosenberg in Baltimore agreed with the prosecutors' request and set bond for Billy Shepherd at $250,000.

Neighbors i the Singing Hill sub-division of White Plains, where homes are valued at about $75,000, said they were surprised and shocked by the news of Paul Shepherd's arrest.

"They're the best neighbors we have had," said L.L. Lamb, who lives across the street from the Shepherd family.

"He's really funny, quick and witty and would do anything for anybody," said next-door neighbor Alberta Hughes. "He was very happy and easy-going. It's hard for us to believe."