One would restrict them to the president and seven other high officials, while another, backed by United Russia, a pro-Kremlin political party, and Mr. Putin, would allow 1,000 blue lights.

Although widely regarded as a pro-Kremlin party, it has already found itself in opposition to the presidential administration on several occasions.

Mr. Gudkov, a member of the pro-Kremlin party that controls Parliament, said in an interview that he had heard "informal reports" about Mr. Rybkin's whereabouts, but had no detailed information.

On Saturday President Vladimir V. Putin meets with the full assembly of the pro-Kremlin party United Russia.

The four pro-Kremlin parties were United Russia, Fair Russia, Agrarian Party of Russia and Civilian Power.

In the elections on Sunday, Russian voters delivered a convincing victory to a pro-Kremlin party that pledged to support Mr. Putin's efforts to secure and stabilize Russia.

The depth of public anger over the new law and the specter of elderly protesters have rattled Mr. Putin's government and United Russia, the pro-Kremlin party that dominates Parliament.

"It's clear to us that administrative resources were widely used to assist pro-Kremlin parties," Mr. Boucher said.

Critics have called the proposal the latest in a series of measures intended to bolster the pro-Kremlin party, United Russia, and diminish political competition.

United Russia, a pro-Kremlin party that unfailingly supports Mr. Putin, controls the Duma and orchestrated the measure's swift approval with little debate.