Federal prosecutors in Baltimore have recommended that the Justice Department ask the full 4th Circuit Court of Appeals to reinstate the political corruption conviction of former Maryland Governor Marvin Mandel.

The recommendation must pass through a long Justice Department chain of command and be approved by the U.S. solicitor general before the government can petition the court for a rehearing.

This is the first step in a long series of decisions prosecutors must make before the Mandel issue is settled. It could not be learned yesterday whether the prosecutors would attempt to retry Mandel -- the key decision they will have to make if they lose on appeal.

Three of the seven 4th Circuit judges, by a 2-to-1 vote, last week overturned the mail fraud and racketeering convictions of the former governor and his five codefendants.

If the 4th Circuit granted the rehearing, the judges then could either reaffirm last week's decision or find that the 1977 convictions were, in fact, valid.

However, few petitions for en banc (full court) rehearings are granted, according to several court observers. If a rehearing request were denied, the government still could ask the U.S. Supreme Court to hear an appeal, seek a retrial or drop the charges entirely.

U.S. Attorney for Maryland Russell T. Baker Jr. and two of the prosecutors who handled the Mandel case, Barnet D. Skolnik and Daniel J. Hurson, decided after studying the appeals opinion to seek a rehearing, and their recommendation was communicated to Justice Department officials, sources said.

All three have refused to comment on what course of action they are pursuing or why they are pursuing it.

Mandel was convicted in August 1977 of mail fraud and racketeering after prosecutors charged that he had accepted $350,000 in gifts, vacations and stock from wealthy friends in return for using his office to enrich their business interests.

But 4th Circuit Judges H. Emory Widener Jr. and Donald S. Russell ruled last week that crucial testimony pointing to Mandel as the man who influenced legislative action for his friends should not have been admitted into evidence. They ruled that the testimony was unreliable because the politicians who gave it did not have firsthand knowledge of the facts.

The judges also found fault with several other procedural rulings by the presiding judge at the Mandel trial.

In a strong dissent, Judge John D. Butzner Jr. said his study of the record convinced him "that the trial judge responsibly discharged his duty."

The prosecutors' judgment of the persuasiveness of Butzner's dissent probably was an important factor in their deliberations on what course of action to follow, a lawyer familiar with the appeals process said.

The deliberations, in general, also would include a study of the makeup of any potential appeals panel, lawyers noted.

One judge on the 4th Circuit has disqualified himself from considering the Mandel case, so any government petition for a full court rehearing would require a favorable vote by four of the remaining six judges.

The Justice Department is facing a Jan. 25 deadline for seeking a rehearing, but several lawyers said the court is liberal in granting extensions, particularly in cases as complex as that of Mandel.