Two senior Republican senators sharply criticized Defense Secretary Pete Hegseth on Wednesday over the Trump administration’s handling of Russia in its efforts to end the war in Ukraine, revealing a deepening public split in the party on foreign policy.

Senator Mitch McConnell — one of three Republicans who opposed Mr. Hegseth’s confirmation in January — opened a Senate budget hearing with a blunt critique of President Trump’s approach to Ukraine.

“It seems to me pretty obvious America’s reputation is on the line,” said Mr. McConnell, the former Senate majority leader who leads the Appropriations Committee’s defense subcommittee. “Will we defend democratic allies against authoritarian aggressors?”

Mr. McConnell, an outspoken hawk on Russia and military issues, has been critical of the Trump administration’s defense spending plan, and countered Mr. Hegseth’s argument that the administration was making the largest investment in the military in 20 years through Mr. Trump’s reconciliation package.

Mr. McConnell, a Kentucky Republican, said that putting military spending into that package and not increasing spending in the regular budget “may well end up functioning as a shell game to avoid making the most significant annual investments that we spent years urging the Biden administration to make.”