President Trump and Defense Secretary Jim Mattis chat during the Inaugural Parade on Jan. 20. (Erik S. Lesser/European Pressphoto Agency)

Defense officials responded to criticism Tuesday that the Trump administration’s proposed $52 billion increase in defense spending next year is too small to deliver on the president’s promise to “rebuild the military,” saying they’ve asked for modest growth now and will likely want even more money in 2019.

The comments came as the administration released its proposed budget for 2018. The White House calls for the Pentagon to receive $639 billion, which represents a 9 percent increase over the Obama administration’s last budget, but a more modest 3 percent increase over what Obama had planned.

“$52 billion, I would argue that isn’t chump change,” said John Roth, the Pentagon’s acting comptroller and chief financial officer, in a news conference. “That’s a pretty significant increase in the defense budget that we’re requesting here. And we’re not done. We’ll take a look once we have the new defense strategy. We’ll look at what appears to be the appropriate amount of resources to support that strategy, and we’ll probably go in with a request that will have some degree of growth.”

The comments come after defense hawks, including Sen. John McCain (R-Ariz.), the chairman of the Senate Armed Services Committee, and Rep. Mac Thornberry (R.-Tex.), chairman of the House Armed Services Committee, have said that Trump isn’t doing enough to bolster the military. Thornberry told an audience at the Brookings Institution, a Washington think tank, on Monday that the plan was “basically the Obama approach, with a little bit more but not much.”

McCain criticized the proposal again Tuesday as inadequate, in a new statement.

“After years of budget cuts amid growing threats around the world, this budget request fails to provide the necessary resources to restore military readiness, rebuild military capacity, and renew our military advantage with investments in modern capabilities,” he said.

Among the proposed Defense Department expenses in 2018 are $10.8 billion to buy 70 more F-35 jets, $5.5 billion for two new Virginia-class submarines, $4.6 billion to put toward the Navy’s next aircraft carrier, the future USS Gerald R. Ford, $4 billion for two new destroyers and $3.1 billion for 15 new KC-46 tanker planes.

Mattis also wants to spend more than $2 billion to buy the maximum number of “preferred munitions” that defense contractors can build, including 12,822 guided aerial bombs known as Joint Direct Attack Munitions (JDAMs), 5,039 small-diameter bombs, 1,397 Hellfire missiles and 39 Tomahawk missiles. They would replenish the Pentagon’s weapons stockpile, which has been used heavily in the three-year-old military campaign against the Islamic State terrorist group, Roth said.

During the presidential campaign, Trump promised a “great rebuilding of the Armed Forces,” drawing from proposals by the conservative Heritage Foundation that could cost between $55 billion and $90 billion per year, according to outside experts. The plan included adding tens of thousands of soldiers until the service reaches 540,000, building the Navy’s fleet out to have at least 350 ships, adding about 100 Air Force fighter or attack jets until the service reaches 1,200, and boosting the number of Marine battalions from 24 to 36, which would include thousands more Marines.

But the proposed budget includes only moderate increases in manpower that Congress already approved. That includes adding 26,000 soldiers until there are 476,000, 5,700 sailors until there are 327,900, 3,000 Marines until there are about 185,000, and 8,100 airmen until there are 325,100.

In light of deep cuts in other parts of Trump’s proposed budget, including education, Medicaid and food stamps, the Pentagon also faced questions Tuesday about why it should get more money at all. Defense officials deflected the inquiries, saying they should be handled by lawmakers as part of the larger debate about how the United States spends money.

“It’s our responsibility to advocate for the force and for the need for a joint force that can do what the nation asks us to do to defend the nation,” said Army Lt. Gen. Anthony R. Ierardi, the director of force structure, resources and assessment for the Joint Chiefs of Staff. “The world is a very dangerous place these days, and so I think there is a compelling — there is, I don’t think, I know there is — a compelling justification for this budget to enhance the readiness of the force.”

The Trump administration is expected to introduce its 2018 budget proposal on May 23, which will likely include major cuts to programs for low-income Americans. (Jenny Starrs/The Washington Post)