URUAPAN, Mexico (AP) _ Opposition parties on Saturday accused the governing Institutional Revolutionary Party of trying to rig a special mayoral election in the second largest city in politically volatile Michoacan state.

The vote in Uruapan was set for Sunday after allegations of fraud and disputes over the results forced the annulment of balloting on Dec. 3.

Such allegations have frequently been made against the governing party, which has ruled Mexico since the party's formation in 1929. Party leaders have pledged to end fraud and corruption within the party.

Jose Rosario Torres Ramos, local chairman of the opposition Revolutionary Democratic Party, said he expects the election to extremely close and it could be decided by a few hundred votes.

Uruapan, a city of 450,000, was one of more than 20 where the leftist Revolutionary Democratic Party challenged victories awarded to the governing party.

The Revolutionary Democratic Party and the conservative National Action Party accused the governing party of removing the names of voters from registration lists and of adding phony names to be used by people recruited to vote for the party.

''People go to pick up the credentials and they aren't there,'' said Juan Antonio Chavez Mendoza, a member of the Revolutionary Democratic Party. He said the governing party distributed 5,000 voting credentials to party loyalists.

Luis Donaldo Colosio, national party leader of the Institutional Revolutionary Party, denied the allegation and said his party ''is confident of an unchallengeable, clear and irrefutable victory.'' He spoke in Guadalajara, the country's second largest city, on Friday.

He accused the opposition of resorting to ''violence and anarchy'' because it has little chance of winning.

Revolutionary Democratic supporters seized city halls in 21 communities after the Dec. 3 elections to protest the results.

Army troops using armored vehicles, firing tear gas and spraying protesters with fire hoses, forced them out four months later. No injuries were reported. Most of those arrested were released a few weeks later.