Reputed organized crime figure Carlos Marcello and the man once the second most powerful figure in Louisiana were found guilty by a federal jury today of plotting to deal in bribery and kickbacks to land state insurance contracts.

Besides Marcello, the jury convicted Charles E. Roemer II, who had been state commissioner of administration. Two other defendants in the so-called "Brilab" case, I. Irving Davidson, a Washington lobbyist, and Vicent A. Marinello, a New Orleans lawyer, were acquitted.

Marcello and Roemer each face a 20-year prison term and a $25,000 fine. When the jurors reported their findings after deliberating 15 hours since Friday, Marcello shook his head and told reporters, "I can't say anything right now."

He had been convicted of one of 12 counts, and Roemer was found guilty of one of four counts. The charges against the men included conspiracy to violate the federal racketeering law, violating the statute and engaging in wire and mail fraud.

The Brilab operation, which ran from 1979 until early 1980, had been set up by two undercover FBI agents posing as insurance salesmen. They were aided by Joseph Hauser, a twice-convicted Los Angeles insurance swindler, who agreed to help them in return for leniency.

The indictment accused them of scheming to use bribes to win a rich state contract for group life insurance which would have brought them a monthly commission of $87,000.