Sicilian police arrested two top Palermo financiers today who until recently were considered untouchable members of the Sicilian establishment, on charges of Mafia-related criminal activity.

The two wealthy cousins, Nino Salvo, 58, and Ignazio Salvo, 56, had controlled most of the island's then-autonomous tax collection agencies until 1982. Their arrest in Palermo comes one week after investigators in the Sicilian capital arrested former Palermo mayor Vito Ciancimino on charges of Mafia activities and illegal capital export.

The jailing of the Salvo cousins and of Ciancimino, who have been transferred to a Rome prison, indicates that information provided to investigators by former Mafia boss Tommaso Buscetta is enabling authorities to make unprecedented inroads into organized crime.

Although hundreds of accused or suspected Mafiosi are behind bars, while others are sought actively by police, the Salvo and Ciancimino arrests represent the first move by Italian judicial authorities against alleged members of the so-called "third level," or top rung, of the Sicilian criminal organization.

All three men have been among the targets of investigations in the Sicilian capital by carabinieri police and treasury police working under the direction of a team of Palermo prosecutors and investigating magistrates, according to judicial sources in Palermo and Rome.

The sources said significant corroborating evidence against the Salvos and Ciancimino was provided recently by Buscetta, who turned informer this summer after his extradition from Brazil.

Buscetta's first revelations led to a dramatic roundup of suspected Mafia underlings in late September and early October, when, armed with 366 arrest warrants, police jailed more than 100 persons.

Police sources have suggested, however, that the latest jailings represent only the beginning of a new phase in painstaking and prolonged investigations now under way in Palermo and Rome.

"So far he's told us only a third about what he knows," said a police source with years of experience in this type of investigation, referring to Buscetta.

The Salvo cousins rule over one of the biggest financial empires in Sicily, where they own industries, hotels and real estate. Although there had been suspicions about their activities before, they had never been arrested.

However, according to judicial sources, new information received from Buscetta over the weekend enabled investigating magistrates to produce arrest warrants. Buscetta, known as "Don Masino" to his Mafia associates, said that during a period in 1981 and 1982 when he was on the run from Italian police, he had been hidden several times in the Salvo cousins' vacation villas in the resort town of Casteldaccia, the sources said.

The magistrates reportedly are skeptical, however, about Buscetta's insistence that he did not know the Salvos personally.

In the case of Ciancimino, until recently probably the most flamboyant politician in Palermo, judicial sources said magistrates had found damning evidence of capital export traced from a check signed by the former mayor, or by one of his sons, that two years ago was found in the pocket of a slain North American Mafioso, Michele Pozza, in Montreal.