Even as the world waited Saturday to hear when President Barack Obama was to order military strikes against Syria's chemical-armed regime,the US leader was already under fire at home.

While the latest opinion polls show that the American public does not even support Obama's plan for a "limited, narrow" operation, his hawkish opponents demanded tougher action.

On Friday, the White House released an intelligence summary that it said showed that Bashar al-Assad's regime killed more than 1,400 civilians in a nerve gas barrage.

Obama said that the United States has a duty to respond, but has promised only a limited operation to punish the use of banned weapons rather than to topple Assad's government.

With Obama cloistered at the White House with his advisors, his former presidential opponent Senator John McCain took to the airwaves to call his plans "shameful."

"The president apparently wants to have a kind of a cosmetic strike, launch a few missiles and then say: 'Well, we responded.'," McCain told chat show host Jay Leno on NBC television.

"This is the same president that, two years ago, said Bashar al-Assad had to go. It's also the president that said that there would be a red line if they used chemical weapons," he said.

"Maybe that red line was written in disappearing ink? I don't know. But we have to be as good as our word. And is there any good options? No."

McCain said that if he were commander-in-chief, as he had hoped to be after the 2008 election he lost to Obama, he would destroy the Syrian regime's airbases and arm rebel fighters.

"To our everlasting shame, not one single weapon from the USA has reached the hands of General Idris and the Free Syrian Army. That is shameful, in my view," he declared.

In May, McCain -- a neoconservative 77-year-old former Vietnam War prisoner of war -- traveled to Syria and met rebel leaders fighting Assad.

He has since become the most strident voice calling for US intervention against Assad's Iranian-backed regime, and speaks for a hawkish Washington faction that feels Obama's caution has weakened America's hand.

Obama's top team -- Secretary of State John Kerry, National Security Advisor Susan Rice and Defense Secretary Chuck Hagel -- was to brief skeptical Republican members of Congress later in the day, as the window for strikes opened.

But, while McCain and his allies think the promised "tailored response" to Assad's gassing of Syrian civilians shamefully weak, many voters and US allies consider it reckless.

British lawmakers voted Thursday to veto their government's plan to join the US-led coalition forming to carry out strikes, leaving France as the only Western ally likely to take part.

And, according to an NBC News opinion poll published Friday, American voters oppose military intervention by a margin of 50 to 42.