President Donald Trump pledged a "renewal of the American spirit", as he tempered his most inflammatory rhetoric while fleshing out his nationalist agenda during a landmark speech to Congress.

Transposing hardline campaign promises into a presidential key, Trump offered the most restrained and detailed explanation yet of his America-first world view.

He criticized threats against Jewish community centers and condemned the seemingly racially-motivated killing of an Indian immigrant, answering calls for him to speak out.

And although the 70-year-old president again promised a hard line on illegal immigration, he couched those policies in economic rather than xenophobic terms, winning sustained applause from the Republican dominated Congress.

"By finally enforcing our immigration laws, we will raise wages, help the unemployed, save billions and billions of dollars, and make our communities safer for everyone," he said.

Putting some policy meat on the bones, he proposed introducing an Australian-style merit-based system to reduce the flow of unskilled workers -- and held out the prospect of a bipartisan compromise with Democrats on root-and-branch immigration reform.

Trump arrived to deliver his maiden address before a chamber filled with lawmakers, Supreme Court Justices, ambassadors and generals, facing historically low approval ratings and embroiled in multiple crises.

Hailing what he called a "new national pride" sweeping the country, he sought to use the pomp of the occasion and the presidential pulpit to reclaim authority and course correct after 40 difficult days.

Discussing trade, Trump even enlisted the help of American icon Abraham Lincoln, echoing what the first Republican president described as "protective policy."

"Lincoln was right -- and it is time we heeded his words," Trump said. "I am not going to let America and its great companies and workers, be taken advantage of anymore."

Looking abroad, Trump softened his criticism of NATO partners and vowed to work with allies in the Muslim world.

But he offered no apologies for emphasizing a world order centered on the nation state.

"My job is not to represent the world. My job is to represent the United States of America," he said.

"But we know that America is better off, when there is less conflict -- not more," he said, promising to "find new friends, and to forge new partnerships, where shared interests align."

- 'Far less dark' -

In Trump's longest speech to date as president he remained largely on message, reading his planned address almost verbatim.

Some women Democratic lawmakers had dressed in white for the occasion, a nod to the suffragette movement and an echo of the substantial opposition the president's policies face.

But Trump struck a compassionate tone at times, embracing family-friendly policies like paid parental leave, and even won cautious praise from Democrats for his attempt at a more optimistic vision for America and his call for unity.

"This was far less dark than the inaugural speech. And he has made an attempt to reach out," said Democrat John Larson of Connecticut. "But the devil is in the details."

According to a CNN instant poll, 57 percent of Americans who tuned in saying they had a very positive reaction to the speech.

Pressing his domestic agenda -- and pleasing mainstream Republicans who reluctantly embraced him -- Trump promised to provide "massive" tax relief for the American middle class and to repeal his predecessor's landmark Obamacare health reform.

"When you get into a job and you do it for a while you become better at it, and I think he's improving every single day," said House Majority Leader Kevin McCarthy.

- Balancing act -

The billionaire's populist economic message was crucial in his November victory over Democrat Hillary Clinton -- helping him sway voters in crucial Rust Belt states Michigan, Ohio and Pennsylvania.

Now his challenge is translating that into tangible policy steps and legislative achievements.

He outlined plans for rebuilding America's creaking infrastructure and for high-stakes tax and healthcare reform.

But on all three issues, Trump faces a difficult balancing act with fellow Republicans, who control both the Senate and House of Representatives.

To succeed, Trump -- the consummate political outsider -- may have to embrace Washington deal-making.

Conservatives are desperate to pull Obamacare out by its roots, but party pragmatists are wary of dismantling a system that helped some 20 million Americans obtain health insurance.

Tensions between the executive branch and the Republican-led Congress are also simmering over Trump's 2018 budget proposal.

Trump wants to hike defense spending by $54 billion, offsetting with cuts in foreign assistance and other non-military spending.

On all these issues Trump offered little detail about how to meet his promises worsening the country's nearly $20 trillion national debt.

"This plan doesn't add up. A third-grade math student can see that you're going to blow a huge hole in the deficit if you do the things the president is talking about," Democratic Senator Chris Van Hollen told AFP.

Source: AFP