Former Maryland governor Marvin Mandrel, who Monday lost his final bid to have his political corruption conviction reserved, is entitled to keep his annual $12,500 gubernatorial pension, the state attorney general ruled yesterday.

State personnel officials last year requested the legal opinion from Maryland Attorney General Stephen Sachs on whether Mandel, who was convicted of racketeering and mail fraud, could keep the pension based on his 10 years as governor.

Sachs found that the pension was part of the former governor's compensation for the job, and thus, could not be terminated because of a criminal conviction.

The U.S. Supreme Court refused Monday that review Mandel's conviction, and the former governor is expected to surrender within 30 days to begin serving a four-year prison term.

But Mandrel had begun collecting the pension in February 1979, one month after an appeals court panel overturned his conviction and he resumed office for the final two days of his term, according to Associate Deputy Attorney General Eleanor Carey.

Later, when the full appeals court reinstated the conviction, state officials requested an opinion on whether the pension should be cut off.

In his opinion, Sachs said there have been legislative attempts to amend the pension laws to require forfeiture when there is a criminal conviction, but those efforts have failed. "Consequently, the conviction of former governor Mandel does not, in our judgement, affect his pension rights," Sachs said.

Mandel receives a $1,042-a-month pension for his 10 years as governor and an additional $533 per month for his 16 years in the House of Delegates.

When his conviction was overturned lat year, Mandel also was awarded about $31,000 in back pay that had been withheld because of his suspension from office.

Carey said yesterday that because he did, in fact, resume office for two days, Mandel probably is entitled to keep the back pay. But that question has not been answered in a formal legal opinion.