Harry W. Rodgers III, a codefendant of former Maryland governor Marvin Mandel in the political corruption scandal that sent both to prison, is scheduled to be freed today by an order issued under protest by the U.S. Parole Commission.

The action set the stage for Mandel, who has been ordered to serve essentially his entire three-year term, to seek an earlier release date. "The rationale is there from a humanitarian and an equity standpoint," said Mandel attorney Bruce Bereano, who intends to request equal treatment for his client.

Under his current parole date, Mandel is not expected to be released from the prison camp at Eglin Air Force Base in Florida until next May.

In ordering Rodgers' release, the three-menber parole panel yielded to a directive from a federal magistrate in Pensacola, Fla., that Rodgers be set free after serving no more than 16 months of his three-year term. The directive cut about four months from Rodgers' sentence.

In announcing their decision, the parole commissioners said they have asked the U.S. solicitor general to appeal it to the 5th U.S. Circuit Court of Appeals, and advised Rodgers he could be returned to prison should the judgment go against him. The magistrate's order "doesn't represent the commission's view of an appropriate decision," the panel asserted.

Rodgers, along with Mandel and four others, was convicted on mail fruad and racketeering charges in August 1977 and entered Eglin in May 1980. The charges stemmed from a scheme in which Mandel tried to help his codefendants, who were secret owners of a racetrack, gain lucrative racing days from the state. Mandel had received gifts and cash from them valued at about $350,000.

John Wilson, a Justice Department spokesman, said the parole panel's reluctant release of Rodgers would have no effect on Mandel's case. "Each person is considered separately," he said.

But Mandel's attorney Bereano called it "very helpful in the sense that they were defendants in the same case, received the same sentence, were accused of the same crimes. This sets the stage for our going to the commission and asking them to take another look at Mandel."

Rodgers won his earlier release date by arguing in federal court that the commission should use guidelines in effect in 1974 when the crimes were committed rather than the more stringent guidelines now in effect.

When the commission still refused to grant an earlier release date, he argued successfully that the board had misapplied the 1974 guidelines.