Though he was only testing it out, little Charles Butler clutched the plastic whistle in his hand at Bancroft Elementary School yesterday and blew as if his life depended on it. He was taking the safety exercise seriously. And in the wake of several recent attacks on District schoolchildren, that is exactly what police and school officials wanted.

"This is not a toy," Bancroft principal Kenneth Milner told his assembly of first through sixth graders. "Be very careful when you blow it . . . . Only use it when there is a threat of danger."

The whistles, a gift from the Fraternal Order of Police, the D.C. department's bargaining agent, were distributed at the Northwest school, where three 5-year-old girls have been molested or abducted in separate incidents.

But they were just one of the safety precautions being taken at schools around the city, where elementary and junior high school officials, police, student patrol monitors and parents are being especially watchful.

Mayor Marion Barry yesterday pledged to lead an all-out effort to stem the rash of attacks, but insisted that the problem has not reached "an epidemic" stage.

Yet, concern over the safety of city children intensified further as police arrested a man who allegedly tried to lure a 12-year-old Clark Elementary School girl into his car as she was walking to school yesterday morning.

Police credited the alert action of a safety patrol boy at the Northwest school -- who got the license number of the car and reported it -- with leading to the arrest.

The suspect, James Edward Robinson, 43, of 1673 Columbia Rd. NW, was arrested and charged with attempted kidnaping, police said.

It was the seventh incident since September in Washington involving an actual or attempted assault on a school child, according to Janis Cromer, spokeswoman for the D.C. school system, who said only four such sex-related incidents were reported during all of last school year.

In the worst recent incident, a 13-year-old Northeast girl, Latanya Lassiter, was fatally stabbed near Woodson Junior High.

Three additional incidents occurred at Bancroft; a 10-year-old girl was raped near the playground of Martin Luther King Jr. Elementary School; and a 16-year-old girl reported being accosted at gunpoint near Ballou Senior High School, although she said she was able to escape unharmed.

Mayor Barry expressed concern about the attacks, but said there is no cause for city-wide alarm.

"There are 90,000 young people who attend our public schools, and thousands of others who attend parochial and private schools," Barry said. "And I believe the great majority of our citizens are safe."

Barry said he and Police Chief Maurice Turner are "doing all we can to apprehend the persons," and he said he would announce additional law-enforcement and safety steps today at a news conference with Turner and public school officials.

The mayor also said that television reports of attacks by "deranged" people are partly to blame, because airing such programs is "glamorizing" violence. " . . . When you all publicize these attacks . . . experts have told me, and I believe them, that spurs others to get ideas that they might not have had, or that spurs other to do it."

Carl Cannon, executive secretary of the board of education, said the schools have received anxious calls from parents who "are responding more to these recent incidents than they did to the reports about asbestos in the schools."

At King elementary school in Southeast, students have had their safety whistles since last spring. Also a gift from the Fraternal Order of Police, they were distributed after earlier assaults on children in that area, according to principal William Dalton.

The 537 youngsters at the school were being closely monitored during their lunch hour yesterday. These students hear an announcement each day to go straight home after school. Dalton said these and other precautions have been in effect for a long time.

Police were on hand at Bancroft yesterday and also at Woodson Junior High, located in Northeast Washington across the street from the Minnesota Avenue Metro station.

At Woodson, principal James Green and Leroy King, a school system security investigator, joined a policeman on the sidewalk yesterday afternoon, and all three kept a close watch as students headed home. Green said several parents have volunteered to help monitor students traveling to and from school, and he said some parents had begun to pick their children up at the end of the day.

The junior high school students weren't given whistles, but they are being encouraged to walk on main roads and with other students when they come and go to school, Green said.

All the "dos and don'ts" for child safety are being stressed again in classrooms around the city, with the theme being that it is better to be safe than sorry.

Some officials, however, worry about the long-range impact of all these warnings.

"We cannot overlook the fact that extra precautions must be taken to provide safety for the children," said James Brown, director of management services for the schools.

"But my concern is that schools are becoming fortresses" he said. "What will this do to the kids in the long run, I wonder? What will the impact be on developing young minds. Schools should be open, free places, not like the CIA or FBI where everybody is watched."