Maryland Gov. Marvin Mandel is the highest ranking government official to be convicted under a seven-year-old federal antiracketering law originally designed as a weapon for combating organized crime, according to Justice Department officials.

Although the antiracketeering statute was part of the Organized Crime Control Act of 1970, it has been used increasingly by federal prosecutors to deal with white-collar crime and political corruption. Mandel and five codefendents were convicted yesterday both of racketeering violations and of mail fraud, a more common charge in political corruption trails.

"It's certainly the first time that a high state official has been convicted under the [antiracketeering] statute." Daniel J. Hurson, one of the assistant U.S. attorneys who prosecuted Mandel, said after the verdicts were announced.

Hurson and other officials also noted that the amount of money Mandel and his codefendents stand to forfeit to the U.S. government as a result of their racketeering conviction apparently is larger than sums forfeited in previous antiracketeering cases.

The antiracketeering law provides - in addition to maximum fines of $25,000 and prison terms of up to 20 years - that violators forfeit their illegally acquired property. The value of the Marlboro Race Track, which apparently would have to be forfeited, has been placed at about $2 million. Another venture apparently subject to forfeiture is the Security Investment Co., from ehich the Social Security Administration leases offices. The company is believed to be worth at least $2 million.

While the political rank of the chief defendant and the sums of money at stake were unusually high, lawyers differed yesterday over whether the convictions broke new legal ground.

Arnold M. Weiner. Mandel's attorney, asserted that the trial raised "a number of unusual and novel questions," including what he termed a "new theory of mail fruad." Such issues apparently will figure in appeals of yesterday's convictions. Weiner did not elaborate yesterday on what he viewed as the novelty of the jury's decision.

Weiner had argued that the antiracketeering law under which Mandel has been convicted applies only to organized crime, rather than to allegations of political corruption.Weiner's contention was rejected in March, 1976 by U.S. District Judge Herbert F. Murray, who was ruling on preliminary motions in the case.

Several lawyers described some of the mail fraud charges as unusual. These alleged that Mandel had defrauded the public by making false statements at press conferences and then sending transcripts of those conferences through the mails.

On the whole, however, government lawyers familiar with racketeering and mail fraud prosecution said yesterday that they saw little legal novelity in the charges on which Mandel and his codefendants were convicted.

"It's not novel," said a congressional staff member who helped draft the 1970 antiracketeering law and is knowledgeable about mail-fraud cases. "The clearest precedent for it is the Kerner case."

Otto Kerner, a former Illinois governor and federal appellate judge, was convicted of mail fraud and other charges ina racetrack stock scandal in 1973. Kerner, who served part of a three-year prison sentence, died last year.

A Justice Department booklet that analyzes the 1970 antiracketeering statute cites a number of previous cases, including prosecution of several government officials.

Five police detectives in Macon, Ga., were convicted under that statute of receiving bribes in return for refraining from enforcing vice laws, the Justice Department analysis notes. A former Small Business Administration official in Richmond. Va., also was convicted under the statute for aiding in providing SBA - guaranteed loans in exchange for bribes.

Among others indicted or convicted under the 1970 antiracketeering law have been officials of a Los Angeles Teamsters local, several Macon. Ga., vending-machine company operators and a Newark. N.J., loan shark.

Justice Department and other lawyers describe the antiracketeering law as a significant tool for use against groups allegedly engaged in crime, whether they are organized gangsters, white-collar criminals or corrupt politicians.

Historically, the Justice Department's analysis notes, most criminal laws were "narrowly" drawn and narrowly interpreted" to deal with specific crimes, such as gambling or extortion. In contrast, the 1970 statute is more broadly framed, to allow prosecutors to demonstrate the existence of a "pattern of racketeering activity."

As one lawyer noted yesterday, the antiracketeering law permits prosecutors to present more evidence to a jury than would be allowed under more narrowly drawn statutes. "The jury gets to find out everything that happened," remarked the lawyer, who asked not to be identified.

He said that the antiracketeering law also differs sublty from conspiracy charges, in part because it spares prosecutors the need to prove that a specific agreement took place among alleged conspirators to engage in criminal activity.

Although the amount of money likely to be forfeited by Mandel and his codefendents is unusually large, other forfeitures have been ordered in previous racketeering cases. The convicted Macon, Ga., vending-machine operators, for example, were required to forfeit $246,000 to the U.S. government, according to the Justice Department.

In contrast with the relatively new antiracketeering law, mail fraud charges have been widely use in prosecuting white-collar criminals and corrupt politicians in recent years, largely because many illegal schemes at some point involve use of the mails.

"It's a tested theory to prosecute politicians," assistant U.S. attorney Hurson said in discussing the use of mail-fraud charges in political corruption trails. Another lawyer described mail-fraud charges as "kind of all purpose" weapons in prosecuting white-collar crime and political corruption.