A cold January day in Prince George's County. A fire breaks out in a two-story Mount Rainer home, where three small children are trapped upstairs.

Firemen rush inside but are beaten back by flames, and the three children die, while their mother, Margie Raffety, helplessly stands outside.

On that much, at least, everyone involved in the 1975 fire seems to agree.

What happened later and why it happened are the questions at issue now in $250,000 damage suit being argued before a U.S. Distict Court jury in Baltimore.

Mrs. Raffety and her husband, Robert, have charged in the suit that their civil rights were violated when they were held for intensive questioning by Prince George's County police and accused of murdering their own children within hours of the Jan. 21, 1975, fire. The Raffetys have since separated.

In his opening statement yesterday, Jayson Amster, the Raffety's attorney, painted a portrait of the "pain, anguish, guilt . . . and fear" he says they experienced during more than 10 hours of questioning after the fire.

At the time, officials had termed the fire arson. No arrests have ever been made, and the case - now more than three years old - remains unsolved.

Still, for the Raffetys, and for the defendants in their suit - Prince George's County detectives David Hatfield and R. Tony Tucker, and fire investigator David Malberg - the case remains very much alive.

Edward Camus, the lawyer for the two police detectives, told the jury yesterday that he will prove his clients "acted reasonably" in their investigation, and "that they were not overbearing."

Amster does not see it that way.

He told the jury that Mrs. Raffety had been induced to come to the county's bureau of investigation against her will, despite the fact that a few hours earlier, "she had been so emotionally distressed that she couldn't speak."

Mrs. Raffety, who had been given a sedative at Prince George's General Hospital and then gone to the home of a friend in Washington, was taken from there to the bureau by two police officers, who are not named as defendants in the suit.

Raffety, a District of Columbia policeman, rushed to the bureau when he learned that his wife had been taken there. Then he, too, was held for questioning.

"They were interrogated separately and accused on several occassions of having murdered their own children," Amster told the jury.

"Independently, and out of a sense of growing frustration and fear, they suggested that they be administered lie detector tests. . . anything to prove their veracity.

"Only after Mrs. Raffety was given a lie detector test and at 3 in the morning were they allowed to go home," Amster said.

Camus maintained in his opening statement that the detectives had been told that Mrs. Raffety made no attempt to rush into her home and save her children. He said that she had pointed firemen toward the wrong bedroom when directing them into the house to rescue the youngsters. He added that Raffety had called his insurance company "to start the claims rolling" within hours after the fire.

Amster had charged that fire ivestigator Malberg determined the fire was arson less than two hours after examining the Raffety's home and before all necessary evidence was available.

Malberg's conclusion "was hasty and without any foundation in evidence," Amster told the jury.

Malberg's lawyer, Gary Neal, said that the "burden of proof" for these charges lies with the Raffetys. Neal said Malberg's action were dictated by the belief that the fire was arson, and the Raffetys will not be able to prove "that this wasn't arson."