REGINA - Jack Layton's refusal to endorse letting the Green party join the televised leaders' debates has not tarnished his party's reputation as an anti-establishment champion of the underdog, the NDP leader insisted Tuesday.

Layton spent the day on the defensive as he was asked to reconcile his party's grassroots, voice-of-the-people image with a surprisingly hardline stand against Green party Leader Elizabeth May.

The NDP isn't about to "let the old interests and powerful sectors" stand in the party's way, Layton told a breakfast crowd of cheering supporters in Regina.

"We're going to take them on," he told about 200 party faithful, including former NDP premier Lorne Calvert, who had jammed the city's famous Free House for pancakes and eggs.

Later, however, he defended his refusal to support May's effort to join the televised debates next month on the grounds that she has already endorsed Liberal Leader Stephane Dion for prime minister.

Layton was asked how he can cast himself as a grassroots leader who would bring change to Ottawa while at the same time defending the status quo when it comes to the debate.

"I'll tell you what the status quo is," the NDP chief fired back -- successive Tory and Liberal governments that represent the old-school establishment.

"We have someone else who wants to be in the debate who actually supports the leader of one of those parties," he said of May.

"I don't agree with that position. I think what we want to do is take on the same old same old, which is the Conservative and Liberal governments in power year after year."

Layton insisted the decision to exclude May was not his, but rather that of the consortium of television networks that will host the event, which takes place Oct. 1-2.

A spokesman for the broadcasters said Monday they opted to exclude May because one or more of the other leaders had refused to accept the invitation if she was allowed to participate.

Layton was one of them; the other is widely presumed to be Prime Minister Stephen Harper.

Harper refused to say Tuesday whether he expressly threatened to boycott the event if May was allowed to participate.

On Monday, however, he said he didn't support the Green party's participation because he expects May to endorse the Liberals before the end of the campaign.

Some NDP supporters at a Monday night rally in Vancouver expressed shock at the party's stand.