SAN SALVADOR, DEC. 22 -- Gen. Adolfo Blandon, the armed forces chief of staff, predicted today that Nicaragua's leftist Sandinista government would not comply with a regional peace plan and may seek to spread Marxism to the rest of Central America.

In a press conference to evaluate the year's military actions, Blandon reported that the U.S.-backed Salvadoran military suffered 3,285 casualties in 1987, and warned that the nation's growing political polarization was aiding the leftist insurgents.

Blandon, flanked by other members of the high command, said 470 Salvadoran soldiers were killed and 2,815 wounded. He said the Army killed 1,004 rebels, wounded 670 and captured 847.

Blandon's comments on both the internal political scene and the peace plan were some of the strongest public statements by the military to date.

Blandon said revelations by Roger Miranda, former top aide to the Nicaraguan defense minister, that Nicaragua had trained 15 Salvadoran rebels in the use of surface-to-air missiles showed the Sandinistas are not sincere about complying with the peace plan.

He said Sandinista requests for advanced weaponry and armored vehicles from the Soviet Union showed Nicaragua was preparing for more than defensive actions, and that they "could be for propagation of Marxism in the rest of Central America."

Military sources said Gen. Carlos Vides Casanova, minister of defense, had flown to Washington last week to be briefed by Miranda on Nicaragua's support for the Salvadoran insurgents.