D.C. Fire Department officials said yesterday they are investigating whether there are grounds for criminal charges as the result of an explosion Monday during a chemistry experiment at a Northwest elementary school that critically injured two 9-year-old students.

Fire officials said they are also investigating the role of D.C. public school administrators in the incident, although the students were attending a special summer session that is not run by the school system.

Meanwhile, school system officials said they are launching an investigation of their own into the explosion at Murch Elementary School, in an attempt to determine whether there was any negligence on the part of the instructors who were in charge of the class. The students were making fireworks at the time of the explosion, officials said.

D.C. School Superintendent Floretta D. McKenzie said the incident might lead to tougher rules on outside programs -- like the "Summer Discovery" program that was meeting at Murch on Monday -- which use school system facilities.

Two 9-year-old boys were admitted to Children's Hospital Monday in critical condition with extensive burns. Their condition was upgraded to serious yesterday, a hospital spokeswoman said. Two other children who suffered minor injuries were scheduled to be released from the hospital late yesterday.

McKenzie said at a news conference that the fireworks experiment "was inappropriate" and had not been approved by school officials.

"We want to review our policies and directives to make sure it doesn't happen again," she said.

There are no city-wide guidelines on outside programs at present, officials said. Principals have been allowed to inspect programs on their own and decide upon their suitability for students, officials said. They added that the plan for the program at Murch, reviewed by the school's principal, did not include a chemistry class.

This summer marks the first year that Murch school has hosted the "Summer Discovery" program for gifted students, ages 8-12. Parents of the 31 youths enrolled in the two-week course paid $165 each in tuition for the program, which is coordinated by Charles Butta, a doctoral candidate at American University. Butta serves as an administrative assistant for a similar summer program that has been operated for six years by professors at the university.

Mary B. Harbeck, supervising director of science programs for city schools, said in an interview that the experiment that was done at Murch on Monday, in which the students were making fireworks called sparklers, "has no scientific value at all."

Harbeck said that shortly after the accident, she interviewed Lou Jagoe, a doctorate candidate at American University who supervised the experiment with an unidentified aide. Harbeck said Jagoe told her he had turned his back just before the explosion.

McKenzie said that if D.C. teachers had been involved in such an experiment, they would face "dire consequences," such as firing. But she said she was "not ready" to decide what action, if any, to take against Butta and Jagoe.

The students had been instructed to mix the combustible substances -- potassium perchlorate, sulfur, charcoal, iron powder and aluminum powder -- in large bowls and grind them as fine as sugar, Butta said.

The explosion was triggered when one student disobeyed instructions and started jabbing a wire from a coat hanger into the mixture, creating a spark that ignited the materials, Butta said.