BELGRADE, Yugoslavia (AP) _ An opposition activist was abducted today in northern Serbia, shortly before a municipal assembly session in which he and other deputies planned to oust a mayor loyal to President Slobodan Milosevic.

The League of Social Democrats of Vojvodina, a strong opposition faction, said Jan Svetlik, a deputy in the local assembly of the northern town of Zrenjanin, was taken from his home by three unidentified men.

The abduction occurred just hours before a session of Zrenjanin's municipal assembly, where Svetlik had recently secured a majority of votes to retake control of the town's government, said League official Emil Fejzulahu.

Fejzulahu said the abduction was a ``brutal way to decrease the number'' of opposition activists in the assembly and prevent the ouster of the current mayor, a member of the ruling Socialists.

The League and several other opposition parties had won 1996 local elections in Zrenjanin, 45 miles north of the capital Belgrade. But they lost control after the 1998 defection of four members who switched allegiance to Milosevic's Socialists, the party that dominates the central government and much of the country.

Recently, however, the four defectors announced they would return, bringing with them two Socialist deputies who decided to switch sides.

Today's session began with protests by the opposition deputies, who demanded Svetlik's immediate release.

The opposition also protested that the Socialist-dominated Zrenjanin government stripped their two defectors of their position as assembly members. The move was apparently meant to further diminish the opposition's narrow majority in the local legislature.

A crowd of several hundred opposition supporters gathered on the town's main square in protest.