The United States had offered to reduce its tariffs on steel, aluminum and autos, and eliminate a recently imposed tariff on Canadian lumber, before negotiations suddenly collapsed last night, Jamieson Greer, the U.S. trade representative, said Saturday.

In an interview with The New York Times, Mr. Greer detailed previously confidential and unreported elements of the U.S. trade offer to Canada, saying those measures would have given Canada the most preferential treatment of any trading partner.

Trade talks between the countries suddenly soured late Friday night, following a week of talks in which negotiators appeared hopeful for an agreement.

Mr. Trump had abruptly threatened Canada with a 50 percent tariff on about $20 billion of its exports in July, in an effort to push the country into making trade concessions and removing certain practices the United States had deemed unfair.

Those tariffs were set to go into effect on the morning of Aug. 19. But on the night before, Mr. Trump delayed the tariffs until Aug. 22, saying that the countries had a deal, “subject to the finalization of documents.”

But over the following days, and particularly late into the night Friday, that consensus crumbled. It fell apart over a series of issues that, individually, may have seemed small but collectively represented a big division over issues of importance to both sides.

Mr. Greer said that the Trump administration had pledged to eliminate the 10 percent tariff on softwood lumber that Mr. Trump imposed last year using a provision known as Section 232.

The United States had also offered to reduce a 25 percent tariff that Mr. Trump put in place last year. But because Canada qualifies for a further reduction when the cars contain any amount of U.S. content, the automotive tariffs could have gone as low as 7 percent, he said.

The United States also offered to lower tariffs on metals, one of Canada’s most important priorities.

U.S. officials offered to cut tariffs on steel to 25 percent from 50 percent for the majority of steel Canada sends to the United States, under what’s known as a tariff-rate quota system. On aluminum, the United States would reduce its tariffs to 25 percent from 50 percent without such a quota limitation, Mr. Greer said.

For downstream products that are made with steel and aluminum, the United States offered to cut those tariffs by anywhere from 10 to 25 percentage points, with the lowest tariffs set at 15 percent.

The Trump administration would also have suspended the 50 percent tariffs that it brought into effect early Saturday morning on Canadian dairy, wine, hockey sticks and others goods, while cooperating on other issues like critical minerals and the transshipment of goods, he said.

The Canadian government did not immediately respond to a request to comment on Mr. Greer’s description of what Canada had left on the table when it suspended talks Friday evening.

In a televised briefing earlier Saturday, Canada’s prime minister, Mark Carney, slammed the U.S. proposal as a “bad deal.” He added, “we cannot accept what they offered and we will not give what they asked.”

Mr. Carney said that Canada had walked away from negotiations not just because it assessed that what was being offered by the United States negotiating team was insufficient, but also because U.S. officials were asking for concessions that Canada was not prepared to make.

He said Canada had equally agreed to meet many American demands, including pulling all its retaliatory tariffs on U.S. steel, aluminum and cars, as well as convince its provinces to restore the sale of U.S. liquor, which most of them have banned.

But, he said, the United States refused to include certain tariff exemptions for heavier trucks. Mr. Carney said the United States also asked for concessions that would affect Canada’s culture and maintenance of protections for the French language and demanded that Canada take out tariffs against non-U.S. trading partners, without offering sufficient benefits for Canada to do so.

“In short, they asked too much and offered too little,” Mr. Carney said in his Saturday address.

Mr. Greer has argued with that assessment. In the interview, he said that the United States offer would “continue their best access and improve it.”

Matina Stevis-Gridneff contribute reporting from Toronto.