The former general manager of an oil recycling company was found guilty tonight of directing the dumping of thousands of gallons of chemical waste into Baltimore Harbor and of improperly disposing of at least 12,000 gallons of PCB-laced oil by selling it as clean oil.

Frank Paul Young Sr. also was convicted by a Baltimore County Circuit Court jury of conspiracy to violate state hazardous waste laws and of conspiracy to obstruct justice for his attempt to cover up the illegal disposal last year in testimony before a grand jury.

Young, 43, who worked his way up from equipment maintenance man to executive at American Recovery Co., Maryland's largest oil recycling firm, sat with his head bowed and his eyes downcast as the jury forewoman read the verdict.

Assistant Attorney General Jane Barrett, who prosecuted the case, said tonight, "I think what's important about this case is that it makes industry executives aware that they will be vigorously prosecuted for violating state hazardous waste laws even if they try to cover up -- that the cover-up will only compound the problem."

Young, through his attorney, Paul Mark Sandler, refused to comment on the verdict and hurriedly left the courthouse. Sandler said he thought the jury, which had deliberated for nearly 10 hours, had been fair. But, he added, he had not yet decided whether to appeal.

Today's verdict capped a six-day trial in which state prosecutors called 28 witnesses and submitted 166 documents as evidence. In contrast, the defense case was short. It included three witnesses and eight documents in evidence. Young did not testify in his defense.

Young's conviction brings to 13 the number of persons in Maryland convicted since 1982 of crimes involving environmental pollution, according to Barrett. Of those, two have received jail sentences and the others have paid fines, been put on probation or ordered to perform community service.

The jury of 10 women and two men, most of whom live in the area of the American Recovery plant near the city harbor in Baltimore County, deliberated nearly 10 hours before convicting Young.

Young, who said earlier in the week that the company had fired him in April and that he had not yet found work, is still under contract with American Recovery as a consultant, according to his attorney.

In February, American Recovery Co. pleaded guilty in Circuit Court to illegally storing and disposing of a wide variety of chemical wastes, including oil laden with cancer-causing PCBs. The company was fined $350,000, the largest fine ever imposed for violation of Maryland environmental laws, according to state officials.

Last December, Young's codefendant, plant manager John W. Driscoll, 35, pleaded guilty to conspiracy to violate hazardous waste laws and to dumping hazardous wastes. As part of his plea bargaining agreement, he was promised that in return for testifying against Young, he will not receive a jail term of longer than 18 months.

Baltimore County Circuit Court Judge Joseph F. Murphy Sr. set sentencing for Nov. 4. The maximum he could receive would be 23 years in prison and $400,000 in fines, but Murphy said in court tonight that if he sends Young to jail, it would not be for more than 18 months.