President Donald Trump's proposal to boost Pentagon spending by $54 billion could be a big win for Connecticut manufacturers that build helicopters, submarines and engines for fighter jets.

But Congress first has to confront a spending cap, or automatic cuts enacted by lawmakers in 2011 to curtail spending over 10 years. Democrats oppose cuts in domestic spending to make room for more money for the Pentagon while two leading Republicans believe the proposed spending increase is insufficient.

Trump's plan for the federal government's budget year that begins Oct. 1 is preliminary, lacks details and will likely be changed by Congress. Still, defense analyst Loren B. Thompson at the Lexington Institute, a public policy institute, said the increased funding could be "very good economic news for Connecticut," particularly at Electric Boat, Pratt & Whitney and Sikorsky.

"More subs in Groton, more jet engines in Middletown, more helicopters in Stratford," he said.

It's not just Connecticut's trio of defense behemoths that could gain from Trump's budget.

Neal Keating, chief executive officer of aerospace manufacturer Kaman Corp., told analysts on a conference call Wednesday that Trump's increase for defense spending "is good for us." The Bloomfield company would benefit from increased spending on its Marine Corps helicopter program shared with Bell Helicopter, he said.

Just approving a budget that would replace spending plans known as continuing resolutions would be an improvement, Keating said.

"But we see certainly advantages to higher defense spending and certainly other key advantages to actually having a budget," he said.

Connecticut's two Democratic U.S. senators oppose cuts in domestic spending to allow for increased military spending.

"I think the concept presented by Donald Trump is a false choice," Sen. Richard Blumenthal said.

For example, cutting workforce training and education would hobble efforts to hire skilled workers to build submarines at Electric Boat, he said.

A spokeswoman said Sen. Chris Murphy believes Trump's plan to "gut domestic investments and slash every nonmilitary foreign policy tool would hurt families and leave us significantly less safe."

The spending cap is "the real stumbling block," said Rep. Joe Courtney, D-2nd District, a member of the House Armed Services Committee.

Despite the lack of details in Trump's budget, Navy and Electric Boat officials have been speaking with each other about what the submarine manufacturer "would have to do to keep up" with increased spending, he said.

Fellow Republicans also are taking potshots at Trump's defense spending plans. Sen. John McCain of Arizona and Rep. Mac Thornberry of Texas — Republicans who head the two congressional Armed Services Committees — say the increase falls short because it amounts to just $19 billion more than what former President Barack Obama proposed.

That amounts to slightly more than a $13 billion aircraft carrier, hardly a massive increase, Blumenthal said.

Bob Ross, executive director of the state Office of Military Affairs, said military contracts awarded to Connecticut companies total $12 billion to $14 billion a year. That number should rise when the new submarine class goes into production.

Some of that work shifts to other states, but the actual amount of work done in Connecticut is higher if all subcontractors are included. Many companies in Connecticut "don't even know they are defense contractors," Ross said, because a product moves through distribution without originating companies realizing where it ends up.

Electric Boat is bracing for a building boom as U.S. military strategy again relies on sea power to face down China, Iran and Russia. The Groton ship builder had been building three or four submarines a year during the Cold War and replacing two a year could lead to a shortage by about 2030, Thompson said.

"If we build only two attack subs a year, it will be real hard to cover the world," he said.

Courant columnist Dan Haar contributed to this story.