President Trump's pledge to unleash $1 trillion in infrastructure spending is generating a flurry of lobbying from an alphabet-soup list of trade groups whose members are jockeying to reap potentially huge benefits.

In the latest and most sweeping publicity effort, the nation's association of civil engineers said Thursday that the nation's roads, dams, airports and water and electrical systems need $4.6 trillion of work -- more than the entire federal government spends in a year.

But that figure, from the American Society of Civil Engineers, is based on estimates that call for much more spending than what federal agencies and other trade groups have said is needed for infrastructure, CNN found.

The discrepancies raise questions about the society's projections -- and its well-known Infrastructure Report Card, which grades the quality of 16 categories of infrastructure every four years. The White House cites the report card on its website.

The overall infrastructure grade was a D+.

Groups such as the engineers society have a clear interest in triggering as much public spending as possible to benefit their members.

"It's not lost on me that they are the ones who are going to be building much of this infrastructure, so it's in their interest to talk down" the quality of infrastructure, said Steve Ellis, vice president of Taxpayers for Common Sense, a nonpartisan group that monitors government spending.

Society officials say the poor quality of U.S. infrastructure hampers economic growth and costs people thousands of dollars a year in extra travel time and car repairs from rutted streets.

"When it comes to your infrastructure, you should be worried," society president Norma Jean Mattei said Thursday.

Among the discrepancies CNN found:

--The engineers society says roads and bridges need $2 trillion in improvements. The Federal Highway Administration says they need $836 billion.

--The engineers society says drinking-water systems need $1 trillion over 25 years to maintain and expand service. The Environmental Protection Agency says they need $384 billion.

--The engineers society says the 15,000 dams most in need of rehabilitation require $45 billion of rebuilding. The Association of State Dam Officials puts the price at less than half that.

A spokeswoman for the engineers society, Lynn Badgley, said the estimates are based on a review of legislation, investment patterns and academic literature. She declined to address specific questions.

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The engineers are not alone in calling attention to infrastructure problems.

An airports organization said Tuesday that $100 billion in infrastructure spending is needed over the next five years. That figure was included in the engineers society report, and represents a huge jump from the group's estimate of $76 billion two years ago.

But the Federal Aviation Administration estimated in September that airports need just $32.5 billion in infrastructure spending over the next five years.

The Airports Council International North America says its survey is "far more comprehensive" than the FAA report and includes projects that the FAA excluded, such as parking facilities and airplane hangars.

Advocacy groups often have an expansive view of infrastructure needs and include in their assessments projects that both repair facilities and expand them, said Beth Osborne, a senior policy adviser at Transportation for America, a nonpartisan group that urges investment in transportation.

Federal agencies typically assess only infrastructure that needs repair, said Osborne, a former assistant secretary at the Transportation Department.

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The engineers society has spent $12 million lobbying in Washington since 1999, federal reports show. The airports council spent $23 million in that period.

Trump's infrastructure pledge has unleashed a groundswell of anticipation from other groups that have testified at recent hearings or written letters. They include the U.S. Chamber of Commerce, the AFL-CIO, FedEx, the American Water Works Association and BMW of North America.

The National Association of Manufacturers recently released a report calling for $1.3 trillion more to be spent over 10 years on transportation infrastructure.

"All the transportation groups get very excited when an administration talks about transportation," Osborne said.

Trump has given few details of his infrastructure plan other than to say he will ask Congress to approve a measure that would enable $1 trillion in spending by both government agencies and the private sector.

The engineers society said that was a good start.

"With the administration, we've had some discussions about the need for investment in infrastructure. They are certainly aware of the report card," society Executive Director Thomas Smith said this morning. "It's been hard to pin down exactly a concrete plan. There's been a lot of focus on a lot of things."

Democrats and Republicans in Congress broadly agree on the need to spend more money on infrastructure, though there is concern that private investors will not want to put their money in projects that may not generate a return.

Ellis said advocacy groups have helped focus lawmakers on the need for infrastructure spending. But the bigger challenge is prioritizing which infrastructure projects to fund first.

"It's not going to be happening all at once," Ellis said. "It's going to be about setting priorities on those investments."

The engineers society suggested the federal government start by giving more money to well-established federal programs that fund infrastructure programs such as roads, water utilities and dams and levees.