Trump pushes Congress for broad bill on guns after school shooting

(Adds additional quotes from meeting, reaction from lawmakers, NRA)

By Roberta Rampton and Ayesha Rascoe

WASHINGTON, Feb 28 (Reuters) - U.S. President Donald Trump on Wednesday went his furthest yet toward endorsing restrictions on gun sales, bucking Republican Party orthodoxy as he challenged lawmakers to go big on legislation he said would help prevent more school shootings.

Trump said he wanted to go beyond a narrowly focused bill to improve background checks for gun buyers that is backed by many of his fellow Republicans and instead develop a comprehensive plan - even if it includes measures opposed by the powerful National Rifle Association gun lobby, which backed his 2016 candidacy.

"I will sign it," Trump said in a freewheeling hour-long discussion at the White House with a group of lawmakers.

Trump had been cautiously weighing changes to gun laws since a gunman killed 17 people at a high school in Parkland, Florida, on Feb. 14, igniting a wave of national student activism in support of firearms restrictions.

During Wednesday's televised session, Trump, who has championed gun rights, embraced broader changes to the background check system than those contained in a proposal from John Cornyn of Texas, the No. 2 Senate Republican.

"You have to be very, very powerful on background checks. Don't be shy," Trump said.

"It would be nice if we could add everything on to it," he said. The White House is set to present a list of Trump's policy decisions on the issue as early as Thursday.

It was unclear whether his fellow Republicans would go along with his newfound enthusiasm, wary of angering voters who fiercely oppose curbs on gun ownership, particularly ahead of the November elections in which the party's control of Congress will be at stake.

Pushing to expand Cornyn's bill, which has been gaining steam in the Senate, could stall its progress.

Cornyn warned Trump against going big, acknowledging his bill was "not the end-all, be-all," but describing it as a politically pragmatic starting point.

"In the past, we've acquiesced to failure, and have not done things that we know were within our power to accomplish," he said at the meeting.

CHIDES LAWMAKERS OVER NRA

It is not the first time Trump has appeared to break with his party's thinking in a quest to make a deal with Democrats.

In January, he met with a bipartisan group on the thorny immigration issue, pledging to "take the heat" if they came up with legislation. He was quickly reined in by conservative hardliners and a deal was never done.

Senate Democratic leader Chuck Schumer praised Trump's ambition on guns, but said in a statement that "the next step is even more important.