* Trump says China to cut import tariffs on U.S.-made autos
* Chinese, U.S. stocks rise, commodities gain
WASHINGTON, Dec 3 (Reuters) - China has made more than $1.2 trillion in additional trade commitments as part of a deal reached by U.S. President Donald Trump and China's Xi Jingping and Beijing has vowed to take immediate steps on those promises.
Trump and Chinese President Xi Jinping agreed to hold off on new tariffs during talks in Argentina on Saturday, declaring a truce following months of escalating tensions on trade and other issues.
Treasury Secretary Steve Mnuchin said on Monday there was a clear shift in tone at Buenos Aires from past discussions with Chinese officials, as Xi offered a clear commitment to open China's markets to U.S. companies.
"They put on the table an offer of over $1.2 trillion in additional commitments. But the details of that still need to be negotiated," Mnuchin told CNBC. "This is the first time that we have a commitment from them that this will be a real agreement."
National Economic Council Director Larry Kudlow said he, Mnuchin and U.S. Trade Representative Robert Lighthizer had lunch with China's vice premier in Argentina and he told them that Beijing would move immediately on the new commitments.
"The history here with China promises is not very good. And we know that," Kudlow said. "However, I will say this: President Xi has never been this involved.
"They cannot slow walk this, stall this, meander this. Their word: immediately."
Kudlow told reporters at the White House that Washington would like to see progress quickly on structural issues, including intellectual property theft and technology transfers. Americans will get majority ownership in companies in China for the first time, which should help address those issues, he said on CNBC.
The United States agreed not to raise tariffs further on Jan. 1, while China agreed to buy more agricultural products from U.S. farmers immediately.
The two sides also agreed to negotiate over the next 90 days to resolve issues of concern raised by the United States including intellectual property protection, non-tariff trade barriers and cyber theft.
The truce boosted global markets on Monday with world stocks up nearly 1 percent. On Wall Street, the Dow Jones Industrial Average rose 0.94 percent at the open and the S&P 500 by 1.10 percent..
U.S. officials will monitor Chinese progress on enforcing the commitments very closely, Kudlow said.
Trump has appointed Lighthizer, one of the administration's most vocal China critics, to oversee the new round of trade talks with China, a White House official and a U.S. official told Reuters on Monday.
The appointment of Lighthizer may signify a harder line in talks with Beijing and marks a shift from past practices where Mnuchin had a lead role.
Lighthizer is an experienced trade negotiator who just completed a new agreement with Canada and Mexico.
"He's the toughest negotiator we've ever at the USTR and he's going to go chapter and verse and get tariffs down, non-tariff barriers down and end all these structural practices that prevent market access," White House trade adviser Peter Navarro told National Public Radio earlier on Monday.
The White House is stepping up efforts to prod other countries to build more vehicles in the United States. Lighthizer and other officials including National Economic Council director Larry Kudlow are set to meet with German automakers on Tuesday, including the chief executives at Volkswagen AG and Daimler AG, people briefed on the matter said.
On Sunday, Trump tweeted that China had agreed to cut import levies on American-made cars.
Chinese regulators did not respond to requests for comment on Trump's tweet on autos tariffs. Neither country had mentioned auto tariffs in their official read-outs of the Trump-Xi meeting. (Reporting by David Lawder and Jeff Mason; Additional reporting by David Lawder and David Shepardson in Washington, Meng Meng and Stella Qiu in Beijing, Andrew Galbraith and David Stanway in Shanghai, and Noah Sin and Anne Marie Roantree in Hong Kong; Writing by Ben Blanchard; Editing by Kim Coghill and Susan Thomas)