MOSCOW — Hundreds of supporters of the Russian opposition leader Aleksei A. Navalny nominated him for president on Sunday, allowing him to ready the endorsement papers required for candidacy and putting pressure on the Kremlin to allow him to run.

Mr. Navalny, one of the most formidable foes President Vladimir V. Putin has faced during 18 years in power, is prohibited from seeking political office because of a criminal conviction that is largely viewed as retribution. However, he could enter the race if he gets special dispensation or the conviction is thrown out.

About 800 Navalny supporters assembled in a giant tent in a snow-covered forest on Sunday for the formal endorsement meeting. His allies said multiple meeting venues had refused to host the gathering.

The election authorities observed the endorsement process, and Mr. Navalny’s representatives planned to file the nomination papers with the Russian Election Commission later Sunday.