A former Firestone Tire and Rubber Co. executive was sentenced to four years in prison and fined the maximum $14,000 in federal court in New York yesterday for stealing $1 million from illegal corporate slush fund he managed.

Robert P. Beasley, 64, of Akron, Ohio, had pleaded guilty to five counts of a 40-count indictment charging that he converted the company funds to his own personal accounts in some 20 banks across the country.

Until he retired in June 1976, Beasley earned $300,000 a year as executive vice president and vice chairman of Firestone.

According to the charges, Beasley used the money to pay off personal loans and purchase various securities.

The case grew out of a Securities and Exchange Commission investigation into political slush funds at several major tire companies.

The SEC approached Firestone in that case, and asked the company to conduct its own internal audit to discover where alleged slush fund political contributions had gone. But, according to SEC documents, when the company asked Beasley where the money had gone, he refused to answer. At that point the SEC referred the case to the U.S. Attorney.

SEC attorneys have repeatedly said that company officials administering illegal slush funds were probably keeping at least some of the money for themselves, but have not been able to acquire proof of many such cases.

The four-year sentence is one of the stiffest ever imposed for white-collar corporate crime, SEC staff members said yesterday.

Beasley could have been sentenced to up 30 years in jail, but Judge Milton Pollack said he took Beasley's age and health into consideration, and mitigated the sentence accordingly. The fine imposed was the maximum allowable.

In a pre-sentencing memorandum, Beasley told the court that Firestone officials had given him implied consent to comingle the slush fund monies into his own personal accounts. He said he established the personal accounts to conceal the illegal funds from the firm's internal auditors and the Internal Revenue Service. He also said he had repaid the funds he took from the company but admitted he could not document that contention.

Assistant U.S. Attorney Tom Fryman, in his pre-sentencing memorandum, called Beasley's contention that the company knew what he was doing, "outrageous in light of the evidence set out in our original sentencing memorandum."

Judge Pollack said before sentencing, "There is no evidence that any of the Firestone people knew that you were dipping into the corporate till."

Pollack further called Beasley " a Dr. Jekyll and Mr. Hyde in your financial dealings with Firestone . . . You have been disloyal and corrupt. You receive $9,900 a month out of a pension plan, yet you have offered no restitution of any kind and you offered no explanation." Beasley, who served in various corporate positions at Firestone since becoming treasurer in 1962, offered several letters of testimonial from prominent people in the business community.

What finally colcluded the case, according to investigators, was an exhaustive 10-month effort by a team of FBI accountants in New York, who searched bank records and created a detailed reconstuction of Beasley's financial records - including every withdrawal of cash.