The U.S. government Tuesday formally presented El Salvador with six heavily armed helicopters and three attack jets for use against rebels in the country's 11-year-old civil war.

U.S. and Salvadoran officials said the shipment was meant to convince rebels of the Farabundo Marti National Liberation Front, or FMLN, to be more flexible in ongoing peace talks."We would like to take it as a message to the FMLN that militarily they will not accomplish anything," said President Alfredo Cristiani. Gen. George A. Joulwan, commander-in-chief of the U.S. Southern Command, said he hoped the U.S. aircraft "will signal to the insurgents that true peace will come only through negotiations, not from the barrel of a gun."

The Salvadoran government and rebels have held numerous rounds of U.N.-mediated peace talks since May 1990, but virtually no progress has been made.

Cristiani, however, said the secret peace talks "have been moving forward, even with the most sensitive issue - military reform."

Salvadoran Col. Maurico Vargas said the six Huey UH-1M helicopters, mounted with Gatling guns, and three A-37 attack jets were an important contribution to the economically weak Salvadoran government.

But he added that the aircraft were obsolete models meant to replace planes and helicopters downed by the rebels or lost to wear and tear.

"We would call it maintenance of the force, but there has been no growth or modernization of the force," Vargas said.

The shipment of planes and helicopters comes after the FMLN upgraded its anti-aircraft capacity, using surface-to-air missiles and improved ground fire techniques to shoot down five helicopters and two planes since November.

Salvadoran pilots have been forced to adopt dangerous new tactics, flying lower to the ground or at night.

Diplomatic sources say the Salvadoran military had asked the United States for newer, more sophisticated Cobra helicopters, but U.S. officials decided to send more of the Vietnam-era Hueys now being used by the Salvadoran forces.