President-elect Donald J. Trump said on Wednesday that his envoy to Russia and Ukraine would be Keith Kellogg, a retired lieutenant general who was a national security adviser to Vice President Mike Pence during the first Trump administration.

The position could play a crucial role in Mr. Trump’s stated plans to broker an end to a war that began nearly three years ago when Russia began its full-scale invasion of Ukraine.

Mr. Trump has not offered details about what kind of peace agreement he envisions, though Ukrainian officials fear that he might slash aid to Ukraine and seek to cut a deal unfavorable to Kyiv with President Vladimir V. Putin of Russia.

Mr. Kellogg co-wrote a strategy paper in April that said the United States should focus on achieving a cease-fire and negotiated settlement to the conflict.

The United States “would continue to arm Ukraine and strengthen its defenses to ensure Russia will make no further advances and will not attack again after a cease-fire or peace agreement,” Mr. Kellogg wrote with Fred Fleitz for the America First Policy Institute. “Future American military aid, however, will require Ukraine to participate in peace talks with Russia,” they added.

The Biden administration has rejected calls for a cease-fire as favorable to Russia and has not used American aid to pressure Kyiv into peace talks.

Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber? Log in.

Want all of The Times? Subscribe.