UNITED NATIONS (AP) _ Nora Astorga, Nicaragua's new U.N. envoy, said Tuesday her country wants negotiations with the United States and is not trying to export its leftist revolution to other Central American nations.

''Revolutions are not exported like Coca Cola or paperbacks,'' said the former underground revolutionary who once lured a Somoza general into a fatal trap.

Addressing a news conference after presenting her credentials to U.N. Secretary-General Javier Perez de Cuellar, Ms. Astorga, 37, said the only thing Nicaragua wants to export is ''our example.''

''I propose to the United States once more that we are willing to sit down and have a fruitful negotiation that leads to the normalization of our relations,'' she said.

She defended Nicaragua's policies and criticized U.S. attempts to overthrow the Sandinista regime with a low-key approach.

Ms. Astorga said no matter how much aid the Contra rebels receive from the United States, they have no chance of winning ''because they have no political or social base.''

She said Nicaragua's goal is a Central America free of all foreign military forces.

Ms. Astorga declined to discuss her role in 1978 when she lured Gen. Reynaldo Perez-Vega, deputy commander of dictator Anastasios Somoza's national guard, to her bedroom where fellow Sandinista revolutionaries slit his throat.

The Reagan administration refused to accept Ms. Astorga in 1984 as Nicaraguan ambassador to Washington because of her role in the Perez killing.

The new envoy said she believed she was named as ambassador to the United Nations because of her five years experience as deputy foreign minister and because of the importance Nicaragua attaches to the world body.