A fire that gutted a fourth floor classroom at Howard University Hospital and injured 10 persons late Monday night was caused by arsonists, fire officials reported yesterday.

Hospital officials said the fire is the most serious in a series of incidents that have plagued the hospital since last Thursday when about two-dozen hospital guards went on strike.

Haynes Rice, assistant administrator of the hospital said two bomb threats, three false fire alarms and slashed tires on two trucks used to cross the guards' picket line have hampered hospital operations since the strike began.

Fire officials said yesterday they are investigating possible ties between the strike and the fire, but both the officials ans assistant hospital administrator Haynes Rice emphasized they have no evidence of such ties now.

Officials of the Federation of Special Police and Law Enforcement Officers, the union representing the striking guards, could not be reached yesterday for comment.

Among those injured in the fire were three elderly patients, all over 75, who were treated for smoke inhalation after they escaped from a room adjacent to the classroom that burned.

Six firemen also were treated for smoke inhalation after the 10:58 p.m. fire at the hospital, which is located at 2041 Georgia Ave. NW. A nurse was hospitalized when she became faint in the commotion surrounding the blaze.

"If it was arson, it was the most bastardly thing a man could do," said Rice. "Setting a fire in a hospital could end up in mass murder."

The fire, which lasted for about 30 minutes, caused $50,000 damage, according to fire investigator Murdo MacLeay.

MacLeay said a flammable liquid was apparently poured on two mattresses in the classroom and ignited, creating an intense heat.

Roy K. Davenport, 68, a retired deputy assistant secretary of defense who was one of 25 patients evacuated during the fire, said he had taken off his glasses and gotten in bed when the fire alarm sounded.

"The smoke was crawling up the wall and then flowing down in curtain-like fashion," Davenport said.

"There was very little panic," he said yesterday after he was wheeled from the X-ray room in blue pajamas to talk with reporters.

"The nurses were the most disciplined team I have ever seen. It was a tribute to what trained people can do in an emergency," he said.

Forty hospital employees including kitchen and maintenance workers who comprise an emergency fire brigade, were checked by doctors after the fire and found unharmed.

The 40, who practice firedrills monthly, had rushed to the fourth-floor fire, helping nurses to evacuate patients from the adjoining ward, which rapidly was filling with smoke. They also made initial attempts to douse the flames.

When firemen arrived at the hospital, they wore gas masks to guard against toxic fumes from burning mannequins and plastic bed coverings in the classroom.

The classroom, a mock-up of a hospital patient's room, is used to teach nursing students how to handle patients. The room is approximately 60 feet long and 20 feet wide.

Fire officials reportedly were angered when they learned that three elderly women still were in the ward when firefighters arrived.

Yesterday, hospital administrator Rice, who met with Chief Fire Marshal John Breen to discuss possible motives for the arson, said Breen complimented the hospital's staff for its generally quick action.

2 Policemen Rescue

5 in Burning House

Two policemen rescued five persons from a burning house in Northwest early yesterday morning after two children in pajamas flagged down their scout car, police reported.

Police Officers Lowell K. Duckett and Michael W. Duglass entered the burning house at 1643 13th St. NW, after the children, who were awakened by the explosion of an oil burner, ran from the house and told the officers that their relatives were still asleep inside, according to police.

The officers rescued the five adults before Officer Duglass collapsed and was himself rescued by firemen from the third floor of the burning house, officials said.

Officials said the fire did $25,000 in damage.

The firemen placed a 30-foot ladder against the building to get to the third floor of the house. The fire had forced the residents to go to the third floor to escape the flames.