Mr. Lighthizer — whose top deputy will meet with Chinese officials this week ahead of more high-level talks in February — has played down any differences with Mr. Trump and views his role as ultimately executing the directive of his boss. But the trade representative, who declined to be interviewed, has told friends and associates that he is intent on preventing the president from being talked into accepting “empty promises” like temporary increases in soybean or beef purchases.

Mr. Lighthizer, 71, is pushing for substantive changes, such as forcing China to end its practice of requiring American companies to hand over valuable technology as a condition of doing business there. But after 40 years of dealing with China and watching it dangle promises that do not materialize, Mr. Lighthizer remains deeply skeptical of Beijing and has warned Mr. Trump that the United States may need to exert more pressure through additional tariffs in order to win true concessions.

When Mr. Lighthizer senses that anyone — even Mr. Trump — might be going a little soft on China, he opens a paper-clipped manila folder he totes around and brandishes a single-page, easy-reading chart that lists decades of failed trade negotiations with Beijing, according to administration officials.

“Bob’s attitude toward China is very simple. He wants them to surrender,” said William A. Reinsch, a former federal trade official who met him three decades ago when Mr. Lighthizer was a young aide for former Senator Bob Dole of Kansas. “His negotiating strategy is simple too. He basically gives them a list of things he wants them to do and says, ‘Fix it now.’”

Mr. Trump’s selection of Mr. Lighthizer last month to lead the talks initially spooked markets, which viewed the China skeptic’s appointment as an ominous sign. It also annoyed Chinese officials, who had been talking with the Treasury secretary, Steven Mnuchin, a more moderate voice on trade and the primary point of contact for Liu He, China’s top trade negotiator. Mr. Mnuchin has urged the president to avoid a protracted trade war, even if that entails reaching an interim agreement that leaves some issues unresolved.

Mr. Mnuchin, who attended the G-20 dinner, helped Mr. Trump craft an upbeat assessment declaring the Buenos Aires meeting “highly successful” in the presidential limousine back to the airport, according to a senior administration official.