WASHINGTON — The commandant of the Marines has warned the Pentagon that deployments to the southwest border and funding transfers under the president’s emergency declaration, among other unexpected demands, have posed “unacceptable risk to Marine Corps combat readiness and solvency.”

In two internal memos, Marine Corps Gen. Robert Neller said the “unplanned/unbudgeted” deployment along the border that President Trump ordered last fall, and shifts of other funds to support border security, had forced him to cancel or reduce planned military training in at least five countries and delay urgent repairs at bases.

The border deployment and funding transfers, as well as recovery costs from hurricanes Florence and Michael, new housing allowances and civilian pay raises, are taking a toll on combat readiness, Neller wrote to Acting Defense Secretary Patrick Shanahan and Navy Secretary Richard Spencer.

The Times obtained copies of the memos, dated Feb. 19 and March 18.

Neller, a four-star general, said because of the problems, Marines would not participate in planned training exercises in Indonesia, Scotland and Mongolia, and would reduce their participation in joint exercises with Australia and South Korea.

Marines “rely on the hard, realistic training” of the exercises “to develop the individual and collective skills necessary to prepare for high-end combat,” said Neller, who has been commandant since September 2015.

He complained about canceling or shrinking the Marines’ participation “at a time where we are attempting to double down on strengthening alliances and attracting new partners.”

Shanahan and Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, are scheduled to testify Tuesday before the House Armed Services Committee. Members are likely to ask about Neller’s concerns.

Sen. Richard J. Durbin (D-Ill.), vice chairman of the Defense Appropriations subcommittee, said Neller’s memos showed the danger in diverting Pentagon funds to build Trump’s border wall.

“If the president won’t listen to the American people or Congress, then listen to the commandant of the Marine Corps,” Durbin said in a statement.

While the armed services chiefs often warn of budget shortfalls, independent experts who reviewed Neller’s memos described the language as unusually strong, in particular because it cited the president’s highest-profile political priorities.

“It’s pretty unusual for the commandant to be raising concerns that ... a top political priority for the president is undermining the ability of the Marine Corps to do the training they need,” said Mandy Smithberger, a defense expert at the Project for Government Oversight, a nonpartisan independent watchdog group.

“It looks like from Commandant Neller’s perspective, he does think these policies are undermining readiness,” she added.

“This is a pretty strongly worded memo,” said Todd Harrison, director of defense budget analysis at the Center for Strategic and International Studies, a nonpartisan think tank in Washington.

Hurricane recovery efforts, increases in civilian pay and the military housing allowance are probably the biggest factors in the budget shortfall, he added.

“The incremental cost of the border deployment is likely small compared to these other factors,” he said. “It sounds like there are some bureaucratic politics at work here.”

The border deployment is adding to the strain after hurricanes severely damaged Marine Corps facilities and housing in North Carolina and Georgia, Neller wrote.

Citing limits on his ability to transfer money because of the planned reprogramming under the border emergency, Neller said the Marines already were short $1.3 billion for recovery operations this year with another hurricane season approaching.

“The hurricane season is only three months away,” Neller wrote, “and we have Marines, sailors and civilians working in compromised structures.”

The memos are likely to revive uneasiness on Capitol Hill about the border deployment, which reportedly chafed some military leaders, including James N. Mattis, then secretary of Defense, when Trump first ordered it shortly before the Nov. 6 midterm election.

While the White House insisted that active-duty troops were needed to stave off so-called caravans of migrants from Central America, critics accused him of using the military as props for his political agenda, not for security purposes.

On Oct. 29, Trump tweeted, “This is an invasion of our country and our military is waiting for you!”

He later expanded the deployment to roughly 6,000 troops, drawn from the Marines, Army, Air Force and Navy, and extended their stay through September 2019.

They have assisted the Border Patrol by erecting barricades, flying helicopter support and maintaining vehicles. They are not allowed to detain migrants, seize drugs or carry out law enforcement duties.

The White House and Defense Department have sought to reassure wary lawmakers that the deployment, and the president’s declaration of a national emergency on the border, has not hampered military readiness or effectiveness.

During a visit to a Border Patrol station Thursday in McAllen, Texas, Homeland Security Secretary Kirstjen Nielsen said she talked to Shanahan on a regular basis.

“We continue to work together to find ways to support the border mission,” Nielsen said. “Border security is national security. We shouldn’t pretend that it’s something else, because it’s not — it’s a national security issue.”

She directed questions about Neller’s concerns to the Defense Department. Spokesmen for the Pentagon and Shanahan did not respond to requests for comment.

In an email, a Marine Corps spokesman, Capt. Joseph Butterfield, said Neller’s memos made clear that damage from hurricanes, and not the border deployments, caused “by the far the most significant budgetary pressure.”

Border operations cost about $230 million by the end of January, according to the Pentagon. The cost could grow to about $850 million this year, according to the Center for Strategic and International Studies, a nonpartisan think tank in Washington.

The White House has asked Congress to appropriate a record $718 billion for the Pentagon in 2020, including $9 billion for hurricane relief, border security and backfilling military construction projects whose funding could be raided under the national emergency Trump declared on Feb. 15.

Lawmakers have pressed to learn which military construction projects would be deferred or canceled to divert money that could be used to build Trump’s long-promised border wall under the emergency.

On Monday, the Pentagon sent Congress a list of more than 400 military construction projects around the country and worldwide that could be affected.

The 21-page document cites more than $12.8 billion in projects that could be delayed or canceled under the emergency, including 31 projects totaling $1.1 billion in California.

Congressional approval of the administration’s budget request and backfill is far from assured, given the recent border funding fight that led to a 35-day partial government shutdown, and bipartisan votes in both chambers to block Trump’s use of executive action to get around the congressional appropriations process. Trump vetoed the resolution last week.

Times staff writer Molly Hennessy-Fiske in McAllen, Texas, contributed to this report.