Former President Donald J. Trump is planning an aggressive expansion of his first-term efforts to upend America’s trade policies if he returns to power in 2025 — including imposing a new tax on “most imported goods” that would risk alienating allies and igniting a global trade war.

While the Biden administration has kept tariffs that Mr. Trump imposed on China, Mr. Trump would go far beyond that and try to wrench apart the world’s two largest economies, which exchanged some $758 billion in goods and services last year. Mr. Trump has said he would “enact aggressive new restrictions on Chinese ownership” of a broad range of assets in the United States, bar Americans from investing in China and phase in a complete ban on imports of key categories of Chinese-made goods like electronics, steel and pharmaceuticals.

“We will impose stiff penalties on China and all other nations as they abuse us,” Mr. Trump declared at a recent rally in Durham, N.H.

In an interview, Robert Lighthizer, who was the Trump administration’s top trade negotiator and would most likely play a key role in a second term, gave the most expansive and detailed explanation yet of Mr. Trump’s trade agenda. Mr. Trump’s campaign referred questions for this article to Mr. Lighthizer, and campaign officials were on the phone for the discussion.

Essentially, Mr. Trump’s trade agenda aims at backing the United States away from integration with the global economy and steering the country toward becoming more self-contained: producing a larger share of what it consumes and wielding its might through one-on-one dealings with other countries.

Mr. Trump, who calls himself a “tariff man,” took steps in that direction as president, including placing tariffs on various imports, hamstringing the World Trade Organization and starting a trade war with China. If he is elected, he plans a more audacious intervention in hopes of eliminating the trade deficit and bolstering manufacturing — with potentially seismic consequences for jobs, prices, diplomatic relations and the global trading system.