As the novel coronavirus has swept the globe, Pentagon officials have scrambled to adjust everything from basic training to submarine deployments to prevent the pandemic from taking a lasting toll on the military’s ability to respond to adversaries.

But the covid-19 crisis could yield a different sort of long-term impact on the military, one outside the Pentagon’s ability to control: a possible reduction in military spending resulting from the country’s emerging economic meltdown.

Pentagon leaders are requesting a defense budget of $705 billion for fiscal 2021, representing half of the federal government’s discretionary spending and probably once again ensuring that U.S. military spending is far greater than that of any other country.

But current and former officials say a sustained reduction, even if modest, could make it harder for the Pentagon to achieve its long-deferred goals of modernizing military operations and competing more effectively with China at a time when the United States remains tied down in insurgent conflicts in Afghanistan and the Middle East.

Lawmakers have already approved more than $2 trillion in emergency stimulus spending in measures that are designed to provide a lifeline to revenue-starved states and that have generated debt concerns among fiscal conservatives.

Robert Hale, who served as Pentagon comptroller during the Obama administration and is now an adjunct senior fellow at the Center for a New American Security, said forecasting of a severe economic downturn — including high deficits and high unemployment — could result in a “modest decline” in defense spending in the order of 2 to 3 percent in real terms.

“That will still be very hard for the Pentagon to handle,” Hale said, as it heads into what was already supposed to be a “bow wave” period of large outlays on next-generation bombers, tanker aircraft and other big-ticket items.

The Pentagon spending cuts are expected to be far smaller than those that followed the triggering of automatic budget caps in 2013, called sequestration. But even reductions of a smaller scale could disrupt the department’s plans to implement a 2018 strategy that prioritizes retaining dominance over “great power” competitors.

Even before the pandemic, Pentagon leaders had warned of difficulties ahead as they projected a flattened budget following an increase of about 20 percent between fiscal years 2016 and 2020.

Making the case for the Pentagon’s 2021 budget proposal in early March, Defense Secretary Mark T. Esper told lawmakers that the requested spending level required “many tough decisions to ensure our highest priorities were adequately funded.”

Now, the situation looks far more dire. Speaking in a briefing hosted by the Brookings Institution last week, Esper said he was concerned that the stimulus spending would exacerbate the United States’ debt problem and potentially “throw us off course” at the Defense Department.

“So there is concern there that that may lead to smaller defense budgets in the future at the critical time at which we need to continue making this adjustment, where we look at China, then Russia, as our long-term strategic competitors,” he said.

Reduced spending could represent what experts called a “double whammy” at a time when the military may also be facing a challenge to readiness resulting from the virus, which has delayed or precluded trainings worldwide and reduced the number of recruits.

According to Todd Harrison, director of defense budget analysis at the Center for Strategic and International Studies, fiscal patterns since the late 1970s show that periods of high deficits have been followed by cuts to defense budgets, from big reductions during President Ronald Reagan’s second term in office to the deep declines resulting from sequestration beginning in 2013.

“If we see 2 to 3 percent [cuts] a year over five years, then DOD is going to have to go back and take a new look at its strategy,” Harrison said. While China and Russia would remain top priorities, secondary missions in Africa or Latin America could face more significant cuts, he said.

Counting on a flattened budget, Esper last year ordered a review to identify ways to streamline global military operations and make room for expanded emphasis on China. But potential trimming of U.S. activities in Africa have already raised objections on Capitol Hill, an indication that future attempts to cut missions or weapons programs are likely to encounter congressional resistance.

With less money, those trade-offs could become more dramatic. “They just have to be more ruthless,” Harrison said.

Mackenzie Eaglen, a former congressional adviser on defense matters who is now at the American Enterprise Institute, said there had already been some bipartisan support for constraining defense spending before the covid-19 crisis, potentially including from the president himself. Earlier this year in his State of the Union address, President Trump proclaimed that the military had been “completely rebuilt.

While it’s not clear when lawmakers will make constraining high deficits a political imperative, Eaglen noted, “there are more than just debt pressures on the budget,” she said.

Sen. Jack Reed (R.I.), the ranking Democrat on the Senate Armed Services Committee, said he anticipates “acute pressure” on the defense budget, driven in part by sustained unemployment, increased savings and decreased consumption. “So you’ve got all these huge pressures that you’ll have on the budget, and that will translate to the defense budget,” he said in an interview.

That could be intensified by a possible shift among Americans’ priorities, who in recent decades have associated national security threats largely with terrorist threats overseas. Now, defense spending could become a renewed target.

“I think what you will see is much more of a focus by the American people on, you know, how will you protect me and my hometown,” Reed said. “Now, I think with the pressure on budgets, it’ll be more difficult, probably, to build as fast or as much as they wanted to do.”

Other lawmakers say defense cuts are not inevitable. “The world’s not going to be any safer after COVID,” Rep. Mac Thornberry (Tex.), the top Republican on the House Armed Services Committee, said in a call last week with reporters.

“I think it’s a mistake for DOD or anybody to just reflexively say, ‘Oh my gosh, we’ve had to spend all this money on COVID, so I’m sure we’re going to get another 20 percent cut to our budget,’ ” he said. “That should not be the way they plan.”

Budget experts said that if lawmakers decide to trim military spending, the Pentagon could try, as it has done in the past, to allay the impact by slowing weapons procurement, potentially including decisions to purchase fewer of expensive items such as the F-35 Joint Strike Fighter, or by attempting to accelerate plans to retire older jets or ships.

Hale said the economic situation could have financial silver linings for the military. For example, the military typically spends about $15 billion a year on fuel, but the global oil prices collapse could reduce those costs, he said.

Budget experts said the Pentagon is likely to stick with its pre-coronavirus projections for its fiscal 2022 budget proposal, which the department is now finalizing and which would be included in an overall administration request next year.