On the morning of Nov. 24, Ronald William Pelton sat in a chair in Room 409 of the Annapolis Hilton, his back to the window. Across from him sat FBI agents David Faulkner and Dudley Hodgson, who were to question Pelton for four hours that Sunday morning and for an hour again that evening.

The agents, dressed in sport coats and open shirts, tried to establish a casual atmosphere that day, chatting with Pelton about his job as a yacht salesman and allowing him to leave during the afternoon for a brunch date with his girlfriend.

On the surface the meeting as described in court testimony and documents appeared to be an intimate, low-key interview. But elsewhere on the fourth floor that Sunday, the FBI occupied five other rooms; an FBI polygraph examiner had set up shop in Room 410, and other agents and supervisors were on hand to confer with Faulkner.

The events of that day -- the admissions Pelton allegedly made about selling highly secret U.S. intelligence information to the Soviet Union and the way the FBI agents elicted statements from him -- are expected to be a central focus in his trial on espionage charges, in which opening arguments begin here today in U.S. District Court.

Pelton, one of 11 persons arrested in 1985 in an extraordinary rash of spy cases, has been the object of enormous media attention because of the sensitivity of the information he is alleged to have sold the Soviet Union. His case has generated even more interest with CIA Director William Casey's recent recommendation that the Justice Department prosecute news organizations that report on a U.S. intelligence-gathering project that was compromised as a result of Pelton's alleged activities.

Defense and prosecution lawyers agree that the FBI's interview of Pelton was carefully orchestrated down to the placement of chairs and other furniture in the room, but they disagree on the reasons for the careful staging and on the results.

Pelton's lawyer, Fred Warren Bennett, has said he will argue, as he did in a pretrial hearing on whether Pelton's statements to the agents should be used in the trial, that Pelton's constitutional rights were violated during the interview. Bennett, the chief federal public defender for Maryland, has argued that Pelton was in a "custodial" situation during the interview and therefore should have been formally told of his right to remain silent and to have an attorney present.

Pelton was apprised of his rights only near the end of the interview, after he allegedly made damaging statements about his dealings with the Soviets.

The prosecution is expected to counter that the FBI tried to ensure that Pelton felt free to leave during the interview and that the agents were therefore not obligated to read him his rights earlier.

Bennett maintains that the agents duped Pelton into thinking that they wanted information from him not for purposes of prosecution, but so they could assess his potential for use as a double agent. The prosecution is expected to try to show that the agents were careful not to make promises or guarantees of immunity to Pelton.

Judge Herbert F. Murray has ruled that Pelton's statements to the FBI agent can be used as trial evidence.

Pelton, 44, a communications specialist at the super-secret National Security Agency from 1965 to 1979, is facing one count of conspiring to deliver national defense information to the Soviet Union, four counts of delivering or attempting to deliver that information and one count of transmitting communications intelligence to an unauthorized person. He faces a possible life sentence.

Pelton, who appeared gaunt and drawn during recent court hearings, is "concerned but surprisingly not depressed" about his situation, according to Bennett. On the witness stand last month, Pelton appeared nervous but articulate, and conferred frequently with Bennett at the defense table as he did during jury selection last week.

The jurors will be sequestered for the duration of the trial, which is expected to last five to eight days.

Both Bennett and the two assistant U.S. attorneys prosecuting Pelton have had experience in spy cases.

Bennett, 43, a graduate of George Washington law school, represents John Anthony Walker Jr., who pleaded guilty to selling Navy secrets to the Soviet Union last October. He has a reputation as an able lawyer capable of making impassioned appeals to juries on behalf of his clients.

On the other side of the aisle are two young Harvard-educated prosecutors. John Douglass, lead prosecutor in the Pelton case, is a rising star in the Baltimore U.S. attorney's office who last year assisted in the prosecution of Samuel Loring Morison for giving classified U.S. satellite photos to a British defense magazine. Assisting him is Robert McDonald, who also worked on the Walker case for the U.S. attorney's office.

The list of witnesses the prosecution may call includes Pelton's estranged wife Judith, who has been visiting him every Saturday at the Anne Arundel County Detention Center, and his 21-year-old daughter Paula Pelton White.

In addition to FBI agents, other potential prosecution witnesses include Pelton's former girlfriend, Ann Barry, who, Pelton has testified, introduced him in 1984 to a life style that included heavy consumption of alcohol and other drugs. Brian MacAnanny, a longtime friend of Pelton who employed him as a yacht salesman, is another possible witness.

Bennett has said his potential witnesses include Dana Caro, the ranking FBI official present at the Annapolis Hilton during Pelton's interrogation; the manager of the Annapolis Hilton, and Pelton himself.