FARGO, N.D. (AP) _ Mayor Jon Lindgren has bucked the odds for eight years as the unabashedly liberal leader of a Farm Belt city whose state representatives are mostly Republican.

But now three men, led by a born-again Christian city commissioner, are challenging Lindgren in Tuesday's non-partisan election to head the state's largest city. Not since 1970 has the mayor of Fargo faced more than one opponent.

City Commissioner Jeff Frankhauser, the mayor's most vocal critic, says, ''I think the people of Fargo are tired of Jon pushing his views on social issues rather than trying to accomplish things in city government.''

The other candidates are city Commissioner Phillip Watson and Jerome Reinan, a 22-year-old North Dakota State University student.

Frankhauser, 34, a police officer and self-described evangelical Christian, has clashed with the mayor on many issues since being elected to the commission two years ago.

Their most bitter dispute came after Lindgren signed a proclamation in 1984 honoring the city's homosexual community. Last year, Lindgren issued a second Gay-Lesbian Awareness Week proclamation, so outraging the commission that it rescinded the order.

Lindgren said he has no regrets about the proclamations and, if still in office, would sign a third one if gay leaders asked and the request conformed to city regulations.

''I believe that every citizen and every group of citizens should be treated equally,'' the 47-year-old mayor said. ''One of the reasons I signed the proclamations was to draw attention to the discrimination homosexuals face.''

Frankhauser called the proclamations a disgrace.

''My feeling is that it's honoring people for their sexual preferences, and I don't think that's needed in city government,'' he said. ''I think the mayor of this city needs to be more concerned with things like street projects and police protection, not social issues.''

Frankhauser said that if elected he would not issue proclamations on behalf of the gay community or any other group he disagrees with.

Watson and Reinan believe their presence on the ballot could force a runoff, and neither is declaring defeat.

If no candidate captures capture at least 50 percent of the vote Tuesday, the top two vote-getters would face each other in a runoff in three weeks.

A poll conducted last week for the Fargo Forum, the city's only daily newspaper, found 42.7 percent of the voters questioned supported Lindgren; 35.4 percent were undecided; Frankhauser and Watson each had 8.9 percent and Reinan had 4.05 percent. The margin of error in the telephone poll of 494 voters, taken by Precision Marketing Inc., was 4 percent.

The city of 66,042 people tends to vote Republican; of its state representatives, eight are Republican and three are Democrats.

Watson's campaign has been gaining momentum in recent weeks, and Frankhauser and Lindgren consider him a formidable opponent.

The Forum last week endorsed Watson, 64, calling him a candidate of ''maturity, business acumen and leadership.''

''I'm just trying to get into the runoff,'' Watson said. ''Once I get in there I think I have a chance because I don't think the Lindgren or Frankhauser campaigns want to be there.''

Reinan, who expects to graduate this summer with a degree in university studies, has said that if elected he would not seek re-election because he plans to accomplish everything he sets out to do in one four-year term.

He said that as mayor he would encourage a city manager form of government.

The mayor, a part-time job paying $17,358 a year, is one of five members of the city commission, and has a vote with no greater weight than other commissioners.