NEW YORK (AP) – MSNBC is replacing Keith Olbermann and Chris Matthews as co-anchors of political night coverage with David Gregory, and will use the two newsmen as commentators.

The change reflects tensions between the freewheeling, opinionated MSNBC and the impartial newsgatherers at NBC News. Throughout the primaries and summer, MSNBC argued that Olbermann and Matthews could serve as dispassionate anchors on political news nights and that viewers would accept them in that role, but things fell apart during the conventions.

Gregory, the veteran Washington hand, will anchor MSNBC's coverage of the presidential and vice presidential debates and election night, network spokesman Jeremy Gaines said this week. The change was first reported by The New York Times.

The tipping point appears to have come during the GOP convention when Olbermann criticized MSNBC for showing a September 11-themed video prepared by the Republicans.

MSNBC executives, who had publicly defended their anchors' roles while privately monitoring them throughout the political season, made the change over the weekend after discussions with Olbermann. Despite the controversy around him, Olbermann has been a hero with left-leaning viewers and keyed MSNBC's growth among coveted young viewers.

During her acceptance speech last week, Republican vice presidential candidate Sarah Palin talked about the "Washington elite" not accepting her qualifications for the job. Some delegates on the convention floor began chanting, "N-B-C, N-B-C''.

Olbermann began to have difficulty keeping his opinions in check, or simply stopped trying.

He sarcastically dismissed GOP pundit Pat Buchanan on the air after Buchanan said the Republicans had been enlivened by the entrance of a conservative Republican.

"Those reading US Weekly with the picture of her and her youngest daughter with the word 'scandal' written across it won't be so happy," Olbermann said.

He expressed little sympathy at another point when GOP anger at rumours over the Internet about Palin were being discussed.

"We'll see if people feel sorry for unfounded rumours on the Internet," he said. "If that's the case, Senator Obama's probably standing up and cheering and waiting for people to feel sorry for him."

Perhaps most embarrassing, Joe Scarborough was discussing positive developments in John McCain's campaign at one point when Olbermann was heard on an offstage microphone saying: "Jesus, Joe, why don't you get a shovel?"

Scarborough, a former Republican congressman and host of MSNBC's "Morning Joe'', got in another nasty on-air exchange with MSNBC reporter David Shuster, and Matthews snapped at Olbermann on-air when it appeared

Olbermann was criticising him for talking too much.