WASHINGTON — Lawmakers signaled a difficult battle ahead for the Obama administration’s plan to dramatically overhaul the nation’s military, voicing opposition Tuesday to proposed cuts in benefit packages, long-standing weapons programs and bases that mean money and jobs across America.

The skepticism from both Republicans and Democrats augured poorly for Defense Secretary Chuck Hagel’s vision of shrinking the Army to its smallest size in three-quarters of a century and creating a nimbler force more suited to future threats than the large land wars in Iraq and Afghanistan over the last decade. Tuesday’s advance of a new veterans bill also suggested Congress may be more interested in increasing military spending in a midterm election year.

The cuts “will weaken our nation’s security while the threats we face around the world are becoming more dangerous and complex,” Sens. John McCain and Lindsey Graham, two leading Republican hawks, said in a joint statement. “Now is not the time to embrace a defense posture reminiscent of the years prior to World War II,” they said, without outlining substitute cost reductions.

Although Congress has agreed on keeping next year’s military budget just under $500 billion, major tradeoffs must still be made to get under the cap.

Tensions exist in both parties. Some Republicans are lining up against tea party supporters keen to rein in spending, while Democrats backing the Obama administration must deal with colleagues from military-heavy districts and states fretful about the potential fallout. Automatic spending cuts that landed heavily on the military were only eased somewhat by a budget agreement two months ago.

The evidence since then suggests appetite is waning for difficult decisions on defense reductions.

Two weeks ago, the House and Senate overwhelmingly eliminated a cut in veterans’ benefits of less than 1 percent that lawmakers themselves enacted only in December. On Tuesday, a Democratic bill expanding health, education and other benefits for veterans at a cost of $21 billion over the next decade unanimously cleared an initial hurdle, with the Senate voting 99-0 in favor of starting debate.

“There’s a lot of need in the veterans community,” said Sen. Bernie Sanders, I-Vt., who sponsored the legislation.