The number of Salvadoran soldiers killed during the past year in combat with antigovernment guerrillas doubled the figure from the previous year, and the overall government casualty rate rose by more than three-fourths to 6,815 dead, wounded or missing in action, the Salvadoran defense minister said today.

In a report to the constituent assembly for the 12 months ending June 30, Defense Minister Carlos Eugenio Vides Casanova said that 2,292 troops were killed in action 4,195 were wounded and 328 were listed as missing. During the previous year's fighting, when government troops as well as guerrillas were less aggressive, Army tallies listed 1,073 dead, 2,484 wounded and 270 missing.

The sharp increases reflected the intensity of recent fighting, particularly during guerrilla offensives from October to May, and a series of reverses suffered by the U.S.-backed Army that led to concern within the Reagan administration over the course of the three-year-old civil war.

The casualty count amounted to one-fifth of El Salvador's total 33,000-man military establishment. U.S. military here said the proportion was high compared with other conflicts.

The ratio, surpassing one dead out of every three casualties, was attributable to poor medical care, lack of quick evacuation by helicopter and a predominance of gunshots over less lethal fragmentation wounds, military experts said. By comparison, one U.S. soldier was killed for every eight casualties in Vietnam.

In an effort to reduce the Salvadoran toll, President Reagan dispatched a team of 25 U.S. medics last month to train counterparts in first aid and to improve the system of evacuating wounded from countryside battlefields to hospitals.

Guerrilla casualties are difficult to estimate for purposes of comparison, since even sympathetic military experts doubt official Army claims and reports over the rebels' Radio Venceremos also are subject to skepticism.

In a study drawing on Army figures and Salvadoran press reports, a research team at the Catholic university in San Salvador calculated that 2,433 guerrillas were killed from October through May, the most intense recent period of combat. The Army officially estimated that 2,000 guerrillas were killed in 1982, while the guerrilla leadership admitted to only 214 killed and 500 wounded in the same period.

Reducing the chances of death for wounded Salvadoran government soldiers could play a strong role in improving morale among the Army troops, National Guardsmen, and national and Treasury police who regularly confront guerrilla units, U.S. advisers said at the time.

Vides Casanova, who took over from Jose Guillermo Garcia on April 22 after a mutiny by one officer and threats from another, said of his first annual report to the assembly:

"With the legitimate pride of a soldier and citizen, I wish to declare that despite the difficulties of the situation our country is going through, our armed forces have a highly positive balance in the field of military actions to combat subversion, without neglecting the fundamental factors of discipline, honor, military education and the well- being of their members."

Outside observers, including U.S. military advisers and diplomats here as well as officials in Washington, generally have qualified the results of the past year's combat here as negative, forcing the administration to seek an urgent increase in military aid last spring.

Similarly, the revolt last January by Lt. Col. Sigifredo Ochoa, who called Garcia a "little Hitler" and demanded that he resign immediately, was seen as a blow to military discipline at a time when the Army needed all the efficiency it could muster. Ochoa eventually backed down and was dispatched to a post in Washington without disciplinary action.

More recently, however, a U.S.-promoted "national plan" was launched in San Vicente and Usulutan provinces with what for the last two months has been hailed as relative success. Guerrilla forces faded away as the program began with a sweep by 5,000 troops. Government agencies in cooperation with the Army units began Vietnam-style programs of civic action to encourage popular support.

Vides Casanova referred to the new emphasis, offering it as one of his top three strategy goals.

Although the guerrilla pullback meant the operation started easily, rebel units have mounted several small-scale attacks in the last week, inflicting a score of casualties and raising fears of efforts on a larger scale to disrupt the pacification.

The attacks, including one against a train that still runs from San Salvador to the eastern stretches of the country, marked the possible end of the relative quiet prevailing since the national plan was launched in June.