Former D.C. deputy mayor Ivanhoe Donaldson, who was given a seven-year prison sentence in January after pleading guilty to corruption charges, must serve four years before he can be paroled -- nearly two years more than had been previously announced, according to a recent U.S. Parole Commission ruling.

U.S. District Court Judge Gerhard A. Gesell, in sentencing Donaldson on charges that he defrauded the city government of more than $190,000 and obstructed the investigation of his wrongdoing, sentenced Donaldson under a provision that required him to serve a minimum of one-third of his seven-year sentence, or 28 months.

However, according to Justice Department officials, the Parole Commission has the authority to change a federal prisoner's minimum sentence based on its assessment of the case and recommendations from prosecutors and the defendant's attorneys.

On May 23, the parole commission, whose proceedings are secret, issued an order specifying that Donaldson, D.C. Mayor Marion Barry's former aide and chief political adviser, remain in prison for four years, until Jan. 28, 1990, according to a Justice Department spokesman.

Donaldson is entitled to another hearing before the parole commission in two years, and the panel could decide to alter the release date.

A Donaldson attorney declined to comment yesterday.

U.S. Attorney Joseph diGenova said he is pleased with the decision.

"The 48-month minimum . . . highlights in a very appropriate way the severity of his conduct and the criminality involved," diGenova said. "It sends a very clear signal."

Donaldson, who is assigned to the federal prison in Petersburg, Va., continues to be of interest to federal prosecutors in Washington and elsewhere. In April, he appeared before a federal grand jury here investigating three former top officials in the city Department of Employment Services who were implicated in the Donaldson case.

Donaldson also was recently interviewed by federal authorities in New York in connection with a scandal there that in part involves parking contracts obtained by Datacom Systems Corp., a parking management and collection firm, according to a New York law enforcement official.

Donaldson was a director and part-time consultant for Datacom. According to federal prosecutors here, he received $70,000 from the firm until he severed his connection with it last year. Datacom, a Lockheed Corp. subsidiary that has contracts with numerous cities, has an estimated $4 million in District government contracts.

Also, Donaldson may be interviewed by federal prosecutors in Chicago in connection with a corruption investigation there that also involves parking contracts obtained by Datacom, according to a law enforcement source.

Manuel Valencia, a Datacom spokesman, yesterday repeated earlier statements that Datacom has not done anything improper in Chicago or New York. He said the firm is confident that it will be exonerated in both investigations.

Donaldson helped Datacom officials set up a meeting in late 1983 or 1984 with Chicago Mayor Harold Washington in which Datacom officials were scheduled to make a presentation, Valencia said. However, Mayor Washington canceled the meeting, and Donaldson played no other role there for the firm, according to Valencia. Donaldson and Barry took part in Mayor Washington's hard-fought 1983 campaign.

Valencia said Datacom executive John Brophy, a former D.C. government parking official who recruited Donaldson to work for Datacom, has testified before the Chicago grand jury and has told company officials that he received "very friendly" treatment. "He Brophy came away from that session feeling very upbeat," Valencia said.

Donaldson played no role in New York City for the firm, Valencia said.

In New York, prosecutors in an affidavit made public in court said that a former New York official hired as a consultant by Datacom, Michael Lazar, allegedly paid $20,000 in bribes to a New York parking official to help Datacom get contracts, and that later Stanley Friedman, the Bronx Democratic leader, replaced Lazar "as Datacom's corrupt liaison" to parking officials.

Prosecutors made the comments as part of an effort to block an attempt to sever the trials of Lazar and Friedman, who have pleaded not guilty to corruption charges.

Datacom, in a statement issued following the New York court disclosures, said it has "never paid, directed or approved the payment of any bribes" and that it has cooperated with federal prosecutors in New York "at every step of the way."