The Chilean government today accused the leaders of the opposition Christian Democratic Party subversive of plotting "to bring about the fall of the government."

Government spokesman Gen. Hernan Bejares passed out copies of the alleged plan, which he said had been written by Andres Zaldidar and Tomas Reyes, who were recently elected president and vice president of the Christian Democratic Party.

Earlier in the day, Chilean President Gen. Augusto Pinochet indicated that he may ban all political parties, saying that they are willing "to do anything to return to power," and added that "I believe it is necessary to end them."

Bejares said the Christian Democrat's plans included cooperation with the Communist Party and with "Marxist sectors in the outside world." He said the action had "provoked the condemnation of Chile" in the United Nations Human Rights Commission.

The Christian Democratic Party was decreed to be "in recess" by the military government in September 1973 but has continued a low profile of opposition activities since status but all leftist parties have been banned since the 1973 coup that brought the military to power.

Earlier the government extended for six more months the country's 3 1/2-year-old state of siege which was to have expired today.

The action extends legal restrictions on civil liberties, including a nightly curfew, and arrest without charges, that have been in effect since the military junta overthrew a leftist government in September 1973.

The decree comes as political repression is at its lowest level since the military coup.

Political detentions without charges - once averaging hundreds per month - dropped to zero in the past two months, according to a Catholic Church agency that has kept close track of arrests.

Today's decree contains almost the exact wording as the previous extension ordered last Sept. 11 and says only that "the conditions remain that motivated the declaration of the state of siege in the decree of internal security."