The last man to see Prince George's County police officer Albert M. Claggett IV alive testified yesterday that Claggett wanted "to calm down" an angry Terrence G. Johnson when he took the 15-year-old into a small fingerprinting room at the Hyattsville police station.

In the moments that followed, police officer Steven H. Gibson testified, he "heard scuffling and a knock or a bump or two against the door or wall." Then came a sound "like a book slamming on a table," and then "five bangs I knew were gunshots," Gibson said.

Seconds later, Gibson went into the room and found Claggett lying on his back, mortally wounded.

Gibson, one of three key prosecution witnesses to testify yesterday at Johnson's murder trial, brought tears to the eyes of Claggett's widow and two sisters as he described the events that led to the deaths last June 26 of Claggett and fellow officer James Brian Swart.

Those early morning shootings heightened existing racial tensions in Prince George's County, since Johnson, now 16, is black and the two slain officers were white.

Gibson said on direct examination by state's attorney Arthur A. Marshall Jr. that he had been processing a teen-ager on a trespassing charge when the 26-year-old Claggett and Swart, 25, accompanying Terrence Johnson and his brother Melvin K. Johnson, came into the processing room at about 2 a.m.

"Officer Swart and Mr. Johnson (Terrence) sat down at one of the tables and Swart began questioning him," Gibson said. "Periodically, Mr. Johnson would slide his chair right up next to Swart's. About four or seven times Swart kicked the chair back. Finally, Swart said, "I told you to keep your chair back." At the time, Gibson said, Johnson was handcuffed to the chair.

"A few seconds later I looked up and it appeared Mr. Johnson was lifting his chair as if to hit officer Swart. Both officer Claggett and I went over and we took Mr. Johnson down on the ground in the corner. He was swinging his feet and his hands. The only thing we were trying to do was keep him under control.

"Someone said, 'Where are my (handcuff) keys?' I had keys so I uncuffed him. 'The officer Claggett said, 'Come in here with me.' They entered the (breathalyzer and fingerprint) room and officer Claggett shut the door."

During cross-examination by defense attorney R. Kenneth Mundy, Gibson repeated several times that he did not "consider the scuffling in the small room) to be a fight."

He also said that while he, Claggett and Swart had Johnson pinned in the cormer (still handcuffed to the chair), Melvin Johnson, sitting in a holding room, started yelling, "I can see you beating him, stop beating my brother."

During the cross-examination, Claggett's widow Caroline left the court-room almost running from the room.

Two other witnesses who were in the processing room just before the shootings, James K. Mattocks and Frank E. Halpin, also described Johnson as "uncooperative," but also confirmed parts of Mundy's opening statement when the defense lawyer said Johnson was treated more severely than two young white trespassing suspects also being held.

Mattocks and Halpin, managers of a local swimming pool, were in the station because three persons had been arrested for swimming in the pool after hours.

Both said that none of three persons arrested for trespassing had been handcuffed and confirmed that one of them had offered Johnson a cigarette. only to have Swart say Johnson could not have one.

They also confirmed Gibson's testimony that Johnson at first refused to give his name. However, they contradicted Gibson on one point, saying that Johnson eventually answered Swart's question.

Both remembered seeing Swart pushing Johnson's chair back with his foot several times.Halpin said at one point Johnson said to Swart, "I'd like to see you outside."

Before the scuffle in the corner, the two men left the room at Gibson's request and were standing in the hall with officer Paul Low when the shootings occurred.

Both men also testified that as Johnson came running down the hall after the shooting, "he was clicking the gun again and again." Halpin said Johnson "slid into the wall," and was ubdued by Low after a struggle in which Low hit the youth on the head with his gun.

Both also said that after Johnson had been recaptured and officers had handcuffed the youth's hands behind him, officer Steven Roberts hit him in the stomach several times and kneed him several times. Roberts is expected to testify today.

Testimony was heard today in a courtroom altered to resemble the processing room of the Hyattsville police station as it was on June 26, 1978.

The prosecution produced a replica of the door to the fingerprinting room and the actual door to the holding room where Melvin Johnson was held.

The doors were set up and tape placed on the floor to give the jury an idea of the scene.In order to view the "station" and a diagram of the layout, Judge Jacob S. Levin spent much of the day sitting on a windowsill.

The prosecution is now about halfway through with its case after two days of jury selection and two days of testimony. The strain of this intense trial appears to be building. Yesterday, Mundy, a confirmed nonsmoker. began borrowing cigarettes during recesses.

"We have a long way to go," he said, shaking his head. "It will get more tense before its over."