SANTIAGO, Chile (AP) _ Patricio Aylwin, a former senator who led the opposition's victory over President Augusto Pinochet in last year's referendum, was chosen Sunday as the presidential candidate of the Christian Democratic Party.

The nominaton by the leading opposition party is likely to be followed by an endorsement from the rest of the anti-Pinochet coalition. Pro-government forces also are expected to pick a candidate for the Dec. 14 election.

''I trust my name will be accepted by the other parties'' in the 17-party opposition coalition, Aylwin said after his unanimous nomination by the Christian Democrat's 286-delegate convention.

''I hope we will be able to reach an agreement on a single opposition candidate,'' said Alywin, 70. ''That's what all the parties in the opposition want.''

The 10-hour Christian Democratic gathering at the town of Talagante, 20 miles southwest of Santiago, ended at dawn Sunday with Alywin's nomination.

The nomination was unanimous, party officials said, after at least two other contenders withdrew from the race.

The nomination was expected to restore unity within the opposition coalition, which was badly split in the last three months over the choice of the presidential candidate.

The opposition coalition is to meet next month to decide on a single presidential candidate.

Leaders from virtully all parties in the coalition, which ranges from the center-right to the left, had said before the convention that they wwere prepared to support Aylwin if he was nominated by the Christian Democrats.

The former senator has been criticized, however, by some leftist politicians who say he did not oppose Pinochet's 1973 coup that toppled the elected leftist government of President Salvador Allende.

Allende died in the coup, taking his own life, according to the military's version, which is now widely accepted.

Aylwin emerged as a leading national political figure as chief spokesman for the united opposition during the campaign for last Oct. 5 referendum, in which voters rejected a military proposal to extend Pinochet's term until 1997. The opposition received 3.9 million votes to Pinochet's 3.1 million.

The referendum outcome made the Dec. 14 open presidential election mandatory. Pinochet is barred by the Constitution to seek re-election, but the Constution still guarantees a prominent role for the military in running the country.

Aylwin, considered a moderate, has said the future government's priority tasks include the trial and punishment of those responsible for the massive human rights violations that occurred under the military government.

Aylwin, a law professsor, is a seasoned politician who was president of the Senate before the 1973 coup.