PALERMO, Sicily (AP) _ FBI Director Louis J. Freeh told Italy the United States is ready to help Italy root out its Mafia in a speech paying homage to a slain prosecutor who was a close friend.

''The full power and resources of the United States law enforcement are at your side now and tomorrow,'' Freeh said Sunday. He mentioned the advanced crime scene analysis and genetic tests that helped bring arrests for the May 1992 highway bombing that killed anti-mob prosecutor Giovanni Falcone.

Freeh repeatedly promised to finish the job started by Falcone and fellow prosecutor Paolo Borsellino, who was killed in a bombing in Palermo two months after Falcone's assassination.

The FBI chief laid a bouquet of orange lilies at the spot outside Palermo where Falcone was killed and visited the graves and families of Falcone and Borsellino.

''We will root you out from under every rock, from the dark places where you hide,'' Freeh warned the Mafia in a speech from the altar of a 750-year- old church filled with more than 1,000 people. ''Your old order is doomed.''

American officials have cooperated for decades with Italian investigators. But Freeh's strongly worded message suggested even greater U.S. aid as the mob reels under waves of arrests and of growing ranks of turncoats breaking the code of silence.

A few of the most important Italian mob defectors, including Tommaso Buscetta, have been given new lives in the United States under the U.S. witness protection program.

Freeh, under heavy guard during his two-day visit to Italy, read a list of Mafia victims that included magistrates and priests.

''You ... are on the verge of a truly historic moment - to vanquish once and for all the yoke of Mafia evil which has gripped the neck of decent people everywhere for centuries,'' he said. A statement from President Clinton read at the church instructed American officials ''to do all they can to strengthen'' U.S.-Italian law enforcement links.

''We do not fear you anymore,'' Freeh said of the Mafia. ''We do not respect you. We challenge you and will hunt you down to bring you to justice.''

He added in Italian: ''Sicilians, Italians, be free.''