Emmanuel Macron, the former economy minister, urged the US President not to pull America out of a landmark agreement struck in Paris to combat climate change.
“Mr Trump would be making a grave mistake by going back on his predecessor's commitments towards the climate,” Mr Macron said, while pledging to continue France’s strong relations with the US.
“I will forge a very strategic alliance with our Chinese partner on this subject.”
Mr Macron said he disagreed with Mr Trump’s environmental policies and protectionism but hoped to continue cooperation on intelligence and counter-terror operations.
The President’s threat to impose a border tax on German cars and unravel Barack Obama’s global warming initiatives have unnerved much of Europe.
Mr Macron warned that the EU would have to raise tariffs on American exports if the US did the same on European goods, in line with World Trade Organisation rules.
“I don’t want to go down that path, but we would respond if the wrong choices were made,” he added.
The candidate also took issue with Mr Trump’s economic policies, which he claimed would hurt the spending power of an American middle class dependent on produced in lower-cost countries.
“I think Mr Trump is wrong to advocate protectionism for his own economy,” he added. “The United States is one of the most open economies in the world.”
Mr Macron previously had a dig at the President when he invited American scientists, academics and entrepreneurs at odds with the Trump administration to move to France last month.
The 39-year-old quit François Hollande’s Socialist government and launched his own centre-left En Marche! party to run for the presidency.
Little attention has so far been directed to Mr Macron’s policies but his standing at the head of polls is likely to turn increased scrutiny on the potential president.
Key manifesto points aim to increase national cohesion and put “French values” at the heart of education, while reforming employment, the welfare system and taxation.
Urging French workers to embrace mechanisation – a source of frequent strikes – he said: “Work is going to change and we will be part of that change. We will go with it and we will transform the balance of forces.”
Mr Macron pledged to hire 10,000 more police officers and improve cohesion between security services after a litany of failures identified in the wake of terror attacks in Paris, Nice and elsewhere in France.
He is calling for an “international roadmap” against Islamist extremism but did not vow to extend France’s controversial state of emergency or implement floated measures like removing French citizenship from dual nationals.
As his main rival, conservative former Prime Minister Mr Fillon, is investigated over allegations he paid his wife and children for parliamentary work they did not do, Mr Macron proposed a ban on officials employing relatives and friends.
He also wants to slim down both chambers of the French parliament and prohibit MPs from carrying out consulting work to ensure leaders who are “exemplary and accountable”.
An ardent supporter of the EU, Mr Macron wants to revitalise the “European dream” by boosting the single market and currency in the post-Brexit “Europe of 27”.
His budget programme includes proposed savings of €60bn (£51bn) over five years in austerity measures that could prove controversial, while keeping the national deficit to below 3 per cent of economic output
As Mr Macron was laying out his vision for France, his two rivals were being dragged deeper into scandals over the alleged misuse of public funds.
Mr Fillon has defied pressure to stand down amid a judicial investigation into the “Penelopegate” affair, with a flash opinion poll by Harris Interactive showing that only 25 per cent of people now want him to continue as a candidate.
Members of his own Les Républicains party called for him to leave the race and three top aides have quit the campaign, but with just weeks until the first round of voting on 23 April, there is no time for new primaries.
Mr Fillon denies any wrongdoing and has stepped up his attacks on a French judiciary he insists is biased against him as part of a “political assassination”.
“I have been singled out by the judicial system. It's as if I had to be brought down at all costs,” he said in an interview with the Midi Libre newspaper.
Meanwhile Ms Le Pen, the leader of the Front National, is refusing to attend police questioning over allegations she misused EU funds to pay for parliamentary aides.
In a fresh blow, the European Parliament voted to lift her immunity from prosecution on Thursday, for tweeting gruesome images of Isis brutality – a crime punishable by three years in prison under French law.
Opinion polls predict the first round of the election to be closely fought between Mr Macron and Ms Le Pen, with around a quarter of the vote each and Mr Fillon trailing on 20 per cent.
That would leave Mr Macon and Ms Le Pen in a second-round showdown on 7 May – one the far-right leader is forecast to lose heavily.