Call it the run-on primary. The results of last week's election to choose a Democratic challenger to Mayor Michael R. Bloomberg have politicians, the public and good-government groups pondering whether a process envisioned as a vehicle for electoral reform needs fixing or has even run its course.

For the fourth time in nine mayoral races, the preliminary returns suggested that no candidate had reached the 40 percent threshold required to avoid an automatic runoff between the top two vote-getters. But this time, with Fernando Ferrer tottering only 250 votes shy of that threshold, according to the earliest unofficial count, Representative Anthony D. Weiner decided, in the interests of his party and his own political future, to defer to Mr. Ferrer rather than mount the potentially divisive runoff that Mr. Bloomberg's strategists had been eagerly expecting. (While the latest count now shows Mr. Ferrer barely over 40 percent, final results may not be known until Tuesday.)

Mr. Weiner's beau geste has flummoxed election officials who are debating whether having a runoff is legally up to the voters or the candidates. The decision will depend, in part, on the official vote count, which politicians have been known to interpret flexibly in the past for less noble purposes. That potential legal anomaly is prompting a reassessment of the entire primary runoff process.

Runoffs were instituted in the 1970's in part to assure that a candidate had wide support from the party before heading into a general election. Otherwise, in a field of many Democratic candidates, a politician with a relatively low number of votes could emerge as the party's nominee.

But for the Democrats in recent years, runoffs have increasingly bred division - often along racial and ethnic fault lines. In fact, a runoff, or the threat of one, contributed to the defeat of the candidate of the city's Democratic majority by a Republican in the last two mayoral elections.

It's arguable, meanwhile, whether runoffs have met their stated goal of producing the most representative candidates.

Calls for a runoff were raised in 1965 after Abraham D. Beame won a four-way mayoral primary with 327,934 votes, which, with 32 percent of Democrats voting, meant that only about 14 percent of enrolled party members voted for him. He was defeated that year by John V. Lindsay, a liberal Republican congressman.

The real impetus for runoffs was the 1969 primary victory of Mario A. Procaccino, who tapped into the rage of middle-class white voters outside Manhattan who were rebelling against Mayor Lindsay's brand of liberalism and perceived favoritism toward blacks and Hispanics. Procaccino led a five-man field with 33 percent of the vote but was anathema to many liberal and mainstream Democrats: "If you think my record is that of a bigot, you're out of your mind, your cotton-picking mind," he declared. He lost to Mr. Lindsay, the incumbent (he had been defeated in his own Republican primary and won on the Liberal Party line).

After the recommendation of a bipartisan mayoral panel, whose members included Herman Badillo, the former Bronx borough president, the Legislature imposed a runoff, effective in 1973. Even before the election, Mr. Procaccino challenged its constitutionality, arguing, "How is a poor guy like myself to run in two elections?"

He lost the lawsuit and did not run again for mayor, but Mr. Badillo did. In the 1973 primary, he finished second, with 29 percent, to Mr. Beame's 34 percent. Mr. Badillo, like Mr. Ferrer a Puerto Rican, was defeated after a raucous runoff (some Beame followers, masquerading as fired-up Badillo supporters, brandished bongo drums in white neighborhoods; then, when the diminutive Mr. Beame accused him of racism, Mr. Badillo responded fatally, "You are a malicious little man").

Four years later, Edward I. Koch finished first in a seven-candidate mayoral primary, with only 20 percent, and won a runoff against Mario M. Cuomo, who had 19 percent. Mr. Koch went on to win that November. In 1989, Mr. Koch was defeated for the nomination by David N. Dinkins, who was renominated without a runoff in 1993.

But it is only in recent elections that the runoff has actually undermined Democrats, producing bitter feelings that endured and often exposing searing racial divisions within the party and contributing to their successive defeats in November general elections.

In 1997, Ruth W. Messinger was nearly plunged into a runoff against the Rev. Al Sharpton (she got 39 percent in the preliminary count), but eight days later absentee ballots helped her squeak past 40 percent. He sued, claiming fraud. The lawsuit was dismissed, but the damage was done. The long count weakened Ms. Messinger, and the charges by Mr. Sharpton left black voters, in particular, disaffected. Whatever her chances before the primary, she lost the general election to the incumbent, Rudolph W. Giuliani, a Republican.

In 2001, Mr. Ferrer won the Democratic primary but lost an acrimonious runoff to Mark Green. Lingering anger by Mr. Ferrer's supporters is believed to have seriously damaged Mr. Green in the general election, and he was defeated by Mr. Bloomberg, then a novice politician.

If some people think the system seems broken, there is no shortage of solutions for fixing it.

Among the earliest suggestions in the 1960's was for a runoff if too small a proportion of the electorate turned out. The present system has not improved turnout, to be sure. Last week, Mr. Ferrer received 182,428 votes, with about 17 percent of Democrats voting, which means that about 7 percent of the city's Democrats actually voted for him.

Mr. Green has proposed having an earlier primary and runoff because a late September runoff leaves too little time to raise money and campaign effectively for a contested race in November. He and a number of politicians would also impose an instant runoff, a form of preferential balloting, in which voters can rank their choices in the primary. In other states, that system has passed muster with federal voting rights officials.

The runoff now also applies to the two other citywide offices, comptroller and public advocate, but Jerry H. Goldfeder, a professor of election law at Fordham Law School, would broaden it. Scott Stringer was nominated for Manhattan borough president last week with 26 percent of the 147,650 votes cast, or about 4 percent of Manhattan's voting-age citizens.

Another stated reason for runoffs was that they might increase black and Hispanic representation by encouraging multiethnic and racial coalitions. That rationale was frequently challenged; Mr. Badillo contends he might have won without a runoff in 1973 and testified in a civil rights challenge that the process discriminated against candidates with less money and encouraged negative campaigning (the money problem has been mitigated by public campaign financing).

Mr. Badillo now favors the runoff. "It will require that you build up a larger constituency to win the election rather than a particular group you are appealing to," he said.

Mr. Sharpton, who was opposed to a runoff until he almost found himself qualifying for one in 1997 against Ms. Messinger, these days opposes runoffs. "It gives an advantage to the opposing party, and it only slows down the process," he said.

In fact, leading black political officials and strategists are of mixed mind as to whether runoffs help or hinder minority candidates, particularly now that non-Hispanic white voters will be a minority for the first time this year.

"The playing field has leveled," said Bill Lynch, an adviser to Mr. Ferrer. "It's hard to say whether a runoff helps or hurts so-called minorities. You're finding minority candidates very much players in the regular election."

But Mr. Green argues that there is one compelling reason to keep runoffs - the same one advanced two years ago when the mayor proposed to scrap the primary system and replace it with nonpartisan elections, including a runoff.

"The argument that you don't want a wacko unrepresentative candidate of the party because he or she gets 21 percent far exceeds any competing arguments, especially since it's not at all clear that the runoff system is antiminority," he said. "Beame beat a minority, Green beat a minority, Dinkins and Ferrer won outright. Of the four examples, it's two to two."