Gen. Augusto Pinochet has pledged to remain in office until March 1990, dismissing opposition demands he step down after losing a plebiscite last week on his 15-year-old government.

In a television interview, Pinochet rejected demands for changes in the country's constitution that allows him to continue in power another 17 months.On Wednesday, Pinochet lost a bid for a new eight-year term in a yes-or-no vote. "I have kept my word. I recognized their triumph and will hand over the government on the established day: March 11, 1990," he said.

Under the controversial constitution drafted by the military in 1980, Pinochet must call competitive elections on Dec. 14, 1989, and hand over power three months later.

The 72-year-old Pinochet, who seized power in a bloody 1973 coup, told his supporters he would not give in to opposition demands for free elections to be held as soon as possible.

Following their victory in the plebiscite, a coalition of 16 opposition parties called on the armed forces to negotiate a speedier transition to civilian rule.

"They voted that I should not continue, not for changes in the constitution. If they want changes, they are not going to get them," Pinochet said. "I don't want a disaster to occur. There will be no negotiations."