A prominent Argentine businessman missing for three days is being described here as the possible victim of a politically motivated "disappearance" that could become a severe embarrassment for the military government of Gen. Reynaldo Bignone.

Buenos Aires federal police say they have launched an intensive search for Marcelo Dupont, 46, an advertising executive missing since Thursday evening. Family members have denied the possibility that he disappeared for personal or financial reasons.

Officials of human rights groups here said today they were following the case closely and added that it appeared likely to be politically linked. If so, they said, it would be the most important such case in Argentina in about three years, when disappearances related to the government's campaign against terrorists largely ended.

Dupont is the older brother of Gregorio Dupont, one of several former government officials who recently have stirred a major public furor over past cases of abduction and assassination linked to the military government.

Buenos Aires newspapers gave prominent attention today to accounts by Marcelo Dupont's family members, who have said they will ask a court Monday to require government security officials to say whether they are holding the businessman.

Although the family has not charged military officials with the disappearance publicly, a family member said that Marcelo Dupont told a friend that he believed he was being followed shortly before his disappearance. Dupont reportedly described the car following him as a white Ford Falcon, an Argentine-made vehicle widely associated here with paramilitary forces of both the military and extremist groups.

In recent days, the 6,000 or so documented disappearances--some sources place the figure as high as 15,000--have become a leading political issue in Argentina, and resolution of the charges against the military is considered the most serious obstacle to the government's planned transition to democratic rule in 1984.

Investigations into disappearances of two Argentine Foreign Ministry officials have been reopened by federal judges after public calls for justice by politicians and several former officials of the military government.

Gregorio Dupont, a former official of the Argentine Foreign Ministry, became a major figure in the controversy two weeks ago when he charged that Elena Holmberg, one of the officials who disappeared, had known of financial dealings between Argentina's leftist Montonero terrorists and Emilio Massera, a powerful former Navy commander in chief and military junta member.

Massera has denied the charges repeatedly and last week filed a slander suit against Dupont in a Buenos Aires court.