Five reputed midwestern mob leaders, including Chicago's acting Mafia boss, were convicted yesterday of skimming almost $2 million from a string of Teamster-financed casinos in Las Vegas.

A U.S. District Court jury in Kansas City returned verdicts of guilty on each of eight counts after a four-month trial that produced dramatic testimony of organized crime's alleged influence over the Teamsters' central states pension fund during the 1970s and its continuing control over top Teamsters officials.

Those convicted were Joseph (Doves) Aiuppa, 78, whom the government has described as the acting boss of Chicago's "Outfit"; his underboss, John P. Cerone, 71; two of their top captains, Angelo LaPietra, 65, and Joseph Lombardo, 57, and Milton P. (Maishe) Rockman, 73, reputed financier of the Cleveland Mafia and its liaison with the Teamsters. They face five years in prison and $10,000 fines on each count, one of conspiracy and seven of using facilities in interstate commerce to exert their secret control over the casinos.

The verdicts climaxed a five-year FBI investigation code-named "Strawman" that began inauspiciously in Kansas City in 1978 with an inconclusive murder probe and eventually expanded to more than 4,000 hours of tape-recorded conversations in five states. It represented the midwestern chapter of a nationwide FBI crackdown on organized crime that had produced the convictions of eight reputed Mafia bosses since 1981 as well as a string of even more highly publicized indictments awaiting resolution in New York.

"We certainly have them on the run," said FBI spokesman Lane Bonner. "We're not going to say we've eliminated organized crime. It's too heavily entrenched. But we have had an impact."

In Kansas City, U.S. District Judge Joseph E. Stevens Jr. refused to release any of the defendants on bond pending appeal and ordered them to federal prison at Leavenworth, Kan., to await post-trial hearings. Lombardo has been serving a 15-year prison sentence for a 1982 conviction with former Teamsters president Roy L. Williams, for conspiring to bribe a U.S. senator, but the other four had been free on bond during the trial.

Alan Caplan, Rockman's lawyer, was the only one who had time to argue for his client before the hearings were postponed until Thursday. He said that there was no danger of Rockman fleeing, but prosecutor David B.B. Helfrey argued that "the LCN [La Cosa Nostra or the Mafia, as it is more commonly called] is a very powerful organization" and that there was no guarantee Rockman would not continue his "association" with it.

Citing affidavits from FBI agents as well as Rockman's brother-in-law, former Cleveland Mafia underboss Angelo Lonardo, Helfrey said Rockman was "a professional in avoiding electronic surveillance," as illustrated by his use of "a leak in the Cleveland FBI office" to frustrate a bugging device in his car.

The prosecutor charged, without elaboration, that Rockman's "dangerousness has been exhibited by a number of mob murders in Cleveland in the 1970s."

The trial, which began last Sept. 23 with nine defendants, centered on charges that the Mafia families in Kansas City, Cleveland, Milwaukee and Chicago demanded and got shares of the gambling receipts from Las Vegas casinos that young West Coast businessman Allen Glick had purchased in 1974. Glick, who bought and refurbished the casinos with $82.75 million in mob-approved loans from the Teamsters' pension fund, testified that he soon found he had a new set of "partners" who threatened to kill him if he didn't meet his "obligations."

Witnesses included former Teamsters president Williams, who told how he came to be controlled by Nick Civella, the late crime boss of Kansas City, and how for years he was paid $1,500 a month for approving the Glick loans. Former Cleveland underboss Lonardo testified that he and Rockman had lobbied for the Chicago Mafia's support of Williams' election as Teamsters president in 1981 and then for Jackie Presser in 1983 after Williams' conspiracy conviction.

The jury retired last Thursday to sort out the evidence, including a jigsaw puzzle of code names (Aiuppa was "22," Cerone "21," LaPietra "Pitsacuni" and Rockman "Deerhunter," according to the government. The pension fund trustees were called the "Monkeys.") The jurors announced their verdicts at 9 a.m. yesterday after 30 1/2 hours of deliberations. Judge Stevens praised them for their dedication and told them, "You've made a courageous decision that comports with the evidence."

Defense attorneys indicated they would appeal. "I was surprised by the verdict because I thought we had put on a case that showed some reasonable doubt," Cerone defense lawyer Charles Shaffer said. "And I think the length of the jury's deliberations showed that they had some concern."

Special correspondent Caroline Rooney contributed to this report.