Three years in the making, Discovery Channel’s ambitious “Greatest American” countdown series debuted to disappointing ratings Sunday.

The three-hour premiere was seen by an average of 949,000 viewers and generated a 0.6 household rating, barely building on its “American Chopper” lead-in. The viewership was slightly below the network’s 2005 first-quarter prime-time average of 1 million viewers.

“Greatest American” was announced as an interactive reality series in 2002 to determine the most influential American in history, with viewers nominating candidates in various categories via online and telephone voting. The concept was based on the overseas success of “The Greatest Briton” and, closer to home, “The Greatest Canadian.”

Produced by NBC Entertainment in conjunction with NBC News Productions, the series partnered with AOL and tapped “Today” personality Matt Lauer as host.

The limited series has received a sizable amount of newspaper press as thousands of “Greatest American” nominations were whittled down to a list of 25 finalists.