President Trump points to a reporter as he speaks during a news conference on North American trade Monday in the White House Rose Garden. (Pablo Martinez Monsivais/AP)

President Trump casts his new North American trade agreement as “the biggest trade deal in the United States’ history” — one that would return lost manufacturing jobs to American shores, discourage future outsourcing of factory work, and “send cash and jobs pouring into the United States.”

But many economists and trade experts say the president’s forecast may prove overly optimistic, given the limited changes that are envisioned and the powerful economic forces that already have reshaped regional commerce. While some industries and regions would fare better than others, the sheer size of the $20 trillion U.S. economy will probably swamp those specific effects.

The accord, which the president has christened the U.S.-Mexico-Canada Agreement, would require automobiles to include more North American parts to qualify for duty-free treatment, pry open a sliver of Canada’s dairy market and update trading rules for the Internet economy.

All that earned the administration wary praise Monday from business groups, farmers, investors and even some Democratic lawmakers. But the president’s ebullience about “high-quality American jobs” ushering in “a new dawn for the American auto industry” stood in contrast to the relatively muted assessments of professional economists.

“This isn’t a revolutionary deal. It’s a modification of a deal already in place,” said Eric Winograd, senior U.S. economist at AllianceBernstein, an investment and research firm. “The total economic impact will be very small. I do not expect it to boost the U.S. economy.”

To the degree that it could drive growth, the deal would do so by removing the cloud of uncertainty that Trump has created by unsettling global trade, some economists said. That climate of doubt may have held back investments — so the new deal could perhaps add a tenth of a percentage point to the economy’s growth rate next year, said Chris Rupkey, chief financial economist at MUFG Union Bank.

“We see this rebranded NAFTA agreement as a marketing exercise,” Rupkey said. “The harsh war of words from Trump’s economics team terrified markets, consumers and businesses for a time, but what the U.S. actually got was much more modest than what the angry war of words seemingly demanded.”

On Wall Street, the Dow Jones industrial average rose Monday about 193 points, or less than 1 percent, to close at 26,651.21.

Trump celebrated the new agreement with a White House Rose Garden ceremony in which he said the deal included stronger labor protections and would make it easier for American farmers to sell to Canadian customers.

Other provisions would refresh regional trading rules for a 21st-century economy, providing important clarity for e-commerce retailers as well as data-rich industries such as financial services.

Even some left-leaning economists gave the president credit for bettering the existing trade bargain.

“I’d argue this deal is an improvement, though enforcement will make or break that impression,” said Jared Bernstein, former economic adviser to Vice President Joe Biden.

The administration will probably confront a tough fight for congressional approval next year, when the House of Representatives may be controlled by Democrats. Touting large potential gains from a new trade deal — as President Bill Clinton did in 1993 when he was promoting the North American Free Trade Agreement — will be a central part of the White House campaign.

“We all tend to overstate the impact of trade agreements,” said Mickey Kantor, who led the Clinton administration’s sales pitch for NAFTA, which Trump’s new deal would replace. “You do that for political reasons. But all we do is open ourselves up to criticism and make ourselves look bad.”

As economists and trade analysts sorted through the 1,800-plus pages of the new accord, they saw few signs of major change.

Lorenzo Caliendo, an economics professor at Yale University’s School of Management who co-authored a NAFTA study published in 2015 that concluded each American had gained about $45 a year from that treaty, said the new agreement would “clearly not” return significant numbers of manufacturing jobs to the United States.

The limited differences between the new and old treaties, coupled with changes in the U.S. labor force over the past ­quarter-century, would minimize the economic benefits, Caliendo said. Much of the work that has moved to Mexico since 1994, when the original deal took effect, would be ill-suited for the higher-skilled contemporary U.S. labor force, according to Caliendo.

“I expect very small aggregate effects,” he wrote in an email.

Some of the gains may be important for individual industries or farmers but may not make much of a difference in the overall economy. The president has been especially critical of Canada’s dairy management system, which limits imports to protect domestic farmers’ incomes and has been a particular irritant for U.S. producers in states such as Wisconsin.

As one of the final issues to be resolved, Canada agreed to open roughly 3.5 percent of its dairy market to U.S. farmers.

The auto industry would face some of the biggest adjustments, illustrating how the deal would create winners and losers. The new agreement is widely expected to raise vehicle costs and create more onerous paperwork requirements, especially for the Tier 1 and Tier 2 suppliers that feed major automakers such as General Motors and Ford.

The Trump administration aims to return auto industry jobs to the United States. To encourage that, the new deal stipulates that at least 75 percent of a vehicle — vs. 62.5 percent today — must be produced in the NAFTA region to qualify for duty-free treatment. Another new provision requires at least 40 percent of each automobile to be made by workers earning $16 an hour, far higher than Mexico’s average factory wage.

“The new deal makes it harder to assemble a car in Mexico and export it to the United States and meet the requirements,” said Chad Bown, a senior fellow at the Peterson Institute for International Economics.

At the same time, he said, “carmakers are also less able to buy cheaper parts from European or Asian suppliers.”

Kristin Dziczek of the Center for Automotive Research in Michigan predicts “tens of thousands” of jobs could return out of 375,000 lost over the past two decades but says American consumers would see sticker prices increase by $470 to $2,200 per vehicle.

But while the agreement may create some additional U.S. and Canadian jobs in the short run, companies over time could look to cut costs by using more robots in their factories.

“We do not anticipate an increase in U.S. auto manufacturing employment. Rather, it will result in an advance in the use of robotics and automation in Mexico,” said Joseph Brusuelas, chief economist at audit firm RSM.

Such judgments are shared by key Democrats. Rep. Sander M. Levin (D-Mich.), a prominent voice on trade policy, told reporters Monday that the Trump administration has done “very little” consultation with Democrats and predicted it will have trouble getting the new pact approved if Democrats retake the House.

“If there’s a major change here, and I think there will be, it will be very difficult to try to push through this trade agreement,” Levin said.

The veteran lawmaker, a fierce NAFTA critic, also said the new regional content rules were less onerous than they appeared.

At the moment, more than 2 million vehicles a year are made in the United States and exported, including some at the BMW plant in South Carolina. Another concern is that if costs rise, companies are likely to cease U.S. production and build cars intended for sale overseas in Asia or Eastern Europe instead.

Ford and GM welcomed the deal, but automakers continue to assess the deal’s impact on their business models. It’s not clear whether the incentives to increase production in the United States will outweigh rising costs from additional regulations and higher material prices, some executives said.

“That’s the big question,” said John Bozzella, president of Global Automakers, a trade group. “We just don’t know at this point.”

Erica Werner contributed to this report.