MOSCOW — Moscow is preparing to hold elections for City Council this fall, but the most prominent opposition politicians say they may not get a chance to run.

To compete in the elections in September, candidates not endorsed by a political party are required to collect about 5,000 signatures, depending on the size of their district.

Election officials began checking signatures last week, and have so far registered 187 candidates, all of whom are largely supportive of President Vladimir V. Putin.

But officials have not approved the signatures gathered by the three most well-known opposition figures — Ilya Yashin, a street activist; Lyubov E. Sobol, a lawyer and an ally of the opposition leader Aleksei A. Navalny; and Dmitri G. Gudkov, who until he lost his seat was the last vocal opponent of Mr. Putin in Russia’s national Parliament.