USC's Pat Haden -- Haven't Spoken with Sark Since Firing

USC athletic director Pat Haden says he spent 2 hours trying to call Steve Sarkisian yesterday to personally inform him he was fired ... but Sark never answered his phone ... so he went public instead.

Haden just spoke to the media ... and said once the decision had been made to get rid of Sark, he called, texted and even reached out to Sark's sister to get the coach on the phone -- but nothing worked.

Haden then issued a press release -- so, the assumption is Sark found out he got the ax at the same time everyone else did. Haden says he has still not spoken with Sark.

During the news conference, Haden also explained why he didn't fire Sark after he showed up drunk to a USC event back in August.

Haden says the two had a private conversation where Haden laid out his expectations for him as a coach -- because he truly believed Sark deserved a second chance.

Haden says Sark blew it over the weekend -- when he showed up to the USC football facility in bad shape.