SAN SALVADOR, El Salvador (AP) _ A heavily armed teen-age couple claiming to be leftist guerrillas held more than 900 school children hostage Wednesday and surrendered to the armed forces after more than six hours.

A guerrilla communique late Wednesday denied any connection with the takeover.

The boy and girl left the school in a blue mini-bus belonging to the army, but police sources would not say where they were being taken. There were no reports of injuries.

Gen. Adolfo Blandon, head of the joint chiefs of staff, entered the school to help persuade the couple to end the siege. Monsignor Gregorio Rosa Chavez, auxiliary bishop of San Salvador, also helped.

''I have the impression that they are not guerrillas, because their arguments are too incoherent,'' Rosa Chavez said after the siege ended at about 4:45 p.m. (5:45 p.m. EST.)

The takeover of the San Jacinto school, which includes first through ninth grades, started at about 10:30 a.m. It came a half-hour after rebels in the neighborhood intercepted a police patrol car, killing two officers and wounding four other people.

The two incidents were not related, said Gen. Rinaldo Golcher, chief of the Treasury Police and the top-ranking security officer at the scene.

A Salvadoran colonel who spoke on condition of anonymity said the couple ran to the school after a routine police blockade stopped them outside the Instruction Center of the Armed Forces in the San Jacinto neighborhood.

Golcher said the boy had deserted from the Instruction Center, which is for communications study, three or four days earlier and took two G-3 rifles.

Regional education director Eduardo Alfonso Molina identified him as Juan Francisco Medrano Eraheta and his companion as Gloria Escobar Guzman. He said they were in their teens but their exact ages were not available.

The school's director, Arely de Flores, said the pair pounded on a door and insisted to be let inside because ''they said they wanted us for protection.''

The boy told a reporter of the television newscast Teleprensa, invited to enter the San Jacinto school for an interview, that he was ''strongly armed.''

His G-3 automatic rifle and a long knife were visible. Police agents at the scene said the couple also was armed with one hand grenade.

''So long as they don't take me out of here, not a single child will leave here, and if a single soldier comes in I'm going to let the bullets fly and I'll kill myself and I'll kill the students,'' he said.

At one point, a girl peeked through the bars of a ground floor window and told reporters: ''We are very scared. They threatened to kill us if we talked with you.''

But about four hours after the takeover started, the couple allowed 25 first- and second-graders to leave the building. The children, dressed in beige uniforms with white shirts, were visibly scared.

An hour later, they began to let most of the other students leave, but delayed the release of 47 ninth-graders, students 14 or 15 years old. At about the same time, a group of rescue workers sawed the bars on two windows and carried some children down a ladder to safety.

When Rosa Chavez entered, the rest of the children were freed.

Special anti-terrorist personnel from the army slipped in through windows shortly before the pair gave themselves up.

Golcher said the man was demanding that President Jose Napoleon Duarte and Roman Catholic Archbishop Arturo Rivera Damas come to the school in the working class, south-side neighborhood of San Jacinto.

The security chief said that the man's parents tried to talk him into surrendering, but he refused to give details.

In the interview with Salvadoran television, the man identified himself as ''Alexander Alvarez Cadena, a captain of the guerrillas.''

As the two went into the school, they dropped a bundle of propaganda leaflets of the Farabundo Marti National Liberation Front guerrilla organization, and the boy insisted he was a member.

But a communique from the front, umbrella organization for the five guerrilla groups fighting here, said: ''This act is the total responsibility of the armed forces. Our combatants never carry out such irrational actions, especially against the people.''

Police sources said the attack on the patrol car occurred about two miles from the school. They said four rebels riding in two automobiles intercepted a patrol car, killing two officers and wounding four people.

The war between leftist rebels and the U.S.-supported government now is in its eighth year. Most of the combat in recent years has taken place in rural areas, but there have been some indications that guerrillas may be trying to move their fight back into the cities.