He declared Nato was "no longer obsolete" and dropped his pledge to declare China a currency manipulator.
Mr Trump also said he was no longer opposed to a federal exports agency he once dismissed as "unnecessary".
And the president signalled he was open to reappointing Janet Yellen as head of the Federal Reserve.
Meanwhile, his administration dropped a freeze on federal hiring that it imposed in January.
The about-faces suggest the mercurial Mr Trump may be favouring a more pragmatic, moderate approach to the hardline economic nationalism that helped elect him.
The startling series of flip-flops come amid reports of a titanic White House power struggle between chief strategist Steve Bannon and senior adviser Jared Kushner.
According to the Washington rumour mill, Mr Bannon - the former Breitbart News executive - has been sidelined after falling out with the president's son-in-law, Mr Kushner.
Mr Trump's decision not to label China a "currency manipulator" emerged in an interview with the Wall Street Journal on Wednesday.
That U-turn follows his talks last week with Chinese President Xi Jinping.
Mr Trump repeatedly pledged to label Beijing a "currency manipulator" on his first day in office, during an election campaign when he also accused the Asian powerhouse of "raping" the US.
But experts said a formal declaration to that effect by the Treasury Department could have led to US sanctions, which would have prompted retaliation from Beijing.
Mr Trump's last campaign ad depicted Janet Yellen, head of the Federal Reserve, as a member of a shadowy globalist cabal "who control the levers of power in Washington".
On Wednesday, he told the Wall Street Journal he "respects" the US central bank chief.
He also indicated he might consider reappointing her next year, saying she would not be "toast".
Mr Trump was once highly critical of the Fed, saying its low interest rate policy had hurt savers. Now he says he likes "a low-interest rate policy".
On his first working day in office, Mr Trump signed a presidential memorandum to suspend hiring of non-military federal workers, in a move that delighted small government conservatives.
The order mandated that "no vacant positionsâ€¦ may be filled and no new positions may be created".
But that policy was gone on Wednesday. White House budget director Mick Mulvaney said: "It does not mean that the agencies will be free to hire willy-nilly."
He said they were "replacing it with a smarter plan, a more strategic plan, a more surgical plan".
In the Wall Street Journal interview, the president praised the Export-Import Bank, which he dismissed in August last year as an "unnecessary" agency with "a lot of excess baggage".
The bank, which provides taxpayer-backed loans for the purchase of US exports, is accused by conservatives of corporate cronyism and welfare.
Now he plans to fill two vacancies on its board.
"It turns out that, first of all," Mr Trump told the Journal, "lots of small companies are really helped."
Mr Trump repeatedly questioned the military alliance's purpose during the campaign.
But as he hosted Nato Secretary General Jens Stoltenberg at the White House on Wednesday, the US president said the threat of terrorism had underlined the alliance's importance.
"I said it [Nato] was obsolete," Mr Trump said. "It's no longer obsolete."
CNN political pundit David Gregory says the shifts show Trump is willing to be a dealmaking president.
"He's flexible, perhaps unprincipled, with a pragmatic approach to government," he said.
But he warned that, although tacking back and forth is fine, it is dangerous to be "all over the map" because people stop believing what you say.
Where Trump stands on key issues
What has Trump done so far?
US President Donald Trump has reversed course in the space of 24 hours on an array of populist positions he adopted during the election campaign.