WASHINGTON — White House officials on Thursday informed Congress of plans to cap the federal civilian pay raise at an average of 1.9 percent for 2018 and to limit the military pay raise to 2.1 percent, just below the expected mark.

In a letter to House and Senate leaders, President Donald Trump said the moves are designed to “put our nation on a sustainable fiscal course” while still ensuring wage increases for the government employees.

Both marks are below the mark expected under federal statute. Federal workers had been anticipating a 1.9 percent base pay raise next year and an additional locality pay bump, and military members a 2.4 percent pay raise.

But Trump had signaled earlier this year that both of those figures were too costly for a federal budget already stretched thin.

Congress can override the president and replace both of the pay raises with higher hikes, but progress on a long-term budget plan for fiscal 2018 (which starts Oct. 1) has been stalled for months on Capitol Hill.

In his letter to Congress, Trump said the lower-than-expected raises will not present a hardship to troops or federal employees.

“I strongly support our men and women in uniform, who are the greatest fighting force in the world and the guardians of American freedom,” he wrote. “As our country continues to recover from serious economic conditions affecting the general welfare, we must work to rebuild our military’s readiness and capabilities.”

The 0.3 percentage point difference in the military pay raise is expected to save the Defense Department about $200 million next year and $1.4 billion over the next five years, money that Pentagon planners hope to reinvest in modernization and readiness priorities.

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The base pay raise for federal workers will be 1.4 percent, with an average locality pay add-on of 0.5 percent. That target had been signaled by federal officials for months, despite complaints from unions and advocacy groups that government employees have seen pay hikes below private sector rates for years.

In his letter, Trump said the move “will not materially affect our ability to attract and retain a well-qualified federal workforce.” He has also advocated sharp personnel cuts at a number of government agencies.

“Federal agency budgets could not accommodate such an [anticipated] increase while still maintaining support for key Federal priorities, such as those that advance the safety and security of the American people,” he wrote.

Lawmakers are scheduled to return to Capitol Hill next week and resume negotiations on the fiscal 2018 budget. If they do not pass a long-term plan or short-term spending extension by the end of September, that will trigger a partial government shutdown.