As high-school students in the late 1960s, Ninfa Segarra and Fernando Ferrer fought for the same political causes. They rallied outside the headquarters of the now-defunct Board of Education to demand bilingual student services, and they belonged to the same tight-knit Puerto Rican youth advocacy group, Aspira.

When Mr. Ferrer, now a Democratic candidate for mayor, rose through the political ranks and became borough president of the Bronx, it was his friend Ms. Segarra whom he asked to represent him on the Board of Education they had long fought to influence.

Now, however, four decades since their days as activists in the Puerto Rican youth movement, they are in opposite camps in the race for City Hall. As she did in the 2001 campaign, Ms. Segarra, 54, is acting as an adviser to Mayor Bloomberg, the man Mr. Ferrer is hoping to defeat. She is part of the team trying to help Mr. Bloomberg solidify support in the Hispanic community – support that Mr. Ferrer is relying on to help him win his party’s primary and then the general election.

During an interview late last week, Ms. Segarra said Mr. Bloomberg, who joined the Republican Party before running for office for the first time in 2001, had delivered for the Hispanic community on three fronts: housing, education, and the economy. While those issues affect virtually all demographic groups, many of the city’s newer Hispanic families have been struggling, so the mayor’s initiatives have aided them profoundly, Ms. Segarra said.

She rejects the fire-breathing from Mr. Ferrer, the three other Democratic candidates, and the two Republican hopefuls. They have repeatedly said the mayor, a former businessman and press mogul, is running the city like his own corporation and is unfazed by the views of low- and middle-income residents trying to make ends meet.

“It’s the traditional political carping without a resolution,” Ms. Segarra said over a cup of tea at a diner around the corner from Mr. Bloomberg’s Manhattan campaign office. “For over 30 years the school system in this city was a disaster. In the three years since the mayor took over, he has made remarkable changes.”

The bad blood between her and Mr. Ferrer dates back to 1992, when she was serving as his appointee on the education board. It was shortly after a 1989 change in the City Charter stripped the borough presidents of much of their power over budgets and land use. Political appointments were one of the only remaining sources of clout for the five borough presidents.

Ms. Segarra was publicly at odds with Mr. Ferrer on several issues, but it was her position on an AIDS education program that changed the course of their relationship. At the height of the AIDS epidemic, when Mr. Ferrer, a politically ambitious borough president, was being pressured to ensure a liberal curriculum, Ms. Segarra cast the deciding vote to pass a resolution requiring that all AIDS education stress abstinence from sexual activity over other forms of protection.

Mr. Ferrer called upon her to change her position. She refused, saying that as the parent of an elementary school student, she deemed the material inappropriate. He demanded that she step down and, along with then-Mayor Dinkins, painted her as a renegade. She bucked his request. The back-and-forth was captured in newspaper headlines.

According to published reports, Ms. Segarra called his action “capricious,” and said she would serve out the remainder of her four-year term. After the vote, Mr. Ferrer said of the board: “I find what they did inexplicable.” Speaking of Ms. Segarra, he told Newsday in 1992, “What she’s done is irresponsible, not to mention really bizarre. She’s been all over the place on this issue and I’m deeply upset.”

She shot back with her own statement, which said: “I will not allow the children’s welfare to be sacrificed for the political interests of others. In the words of one of our early patriots, ‘If this be treason, make the most of it.’ “

Other complicated political divisions developed related to sex- and gender-education curricula, such as the fight over “Heather Has Two Mommies,” a book that was being considered as a tool to teach first-graders to respect gay and lesbian couples. Not surprisingly, the rift sent Mr. Ferrer and Ms. Segarra on separate public paths.

Ms. Segarra, who had already served in the Koch administration as head of the Voter Assistance Commission, soon defected to the Giuliani camp. Though retaining her Democratic registration, as she still says she does, she served as deputy mayor for education and human services in his GOP administration for nearly seven years.

“It sort of directed me out of the Democratic Party,” she said.

In 2001, she beat out one of Mr. Ferrer’s appointees, Sandra Lerner, to become president of the Board of Education. Though she was heading the board, she supported Mr. Giuliani’s efforts to abolish it and turn control over to City Hall.

Last week, Ms. Segarra – who at 5-foot-1-inch says she is “average Puerto Rican height” – insisted there was no persistent tension or hard feelings between her and Mr. Ferrer. Their clash, she said, was professional, not personal. She even expressed gratitude to Mr. Ferrer, who is now struggling to maintain his status as the Democratic frontrunner, for the 1990 appointment. Since then, she has held several major government positions, served as an executive at the City University, and run the city’s Police Department Museum.

Along the way, Ms. Segarra, the daughter of a taxi driver and a seamstress, has had her admirers and her critics. Some have said her outspoken, maverick style was a result of passionate beliefs. Others have said it was political opportunism and complained that she turned her back on progressive causes. She equates herself to Mr. Koch, saying she is “a Democrat with common sense.”

Ms. Segarra would not say how much the Bloomberg campaign was paying her. When pressed about why she opted not to support the Hispanic candidate in the mayoral race, she said it was a case of two different views of the city.

“The view of the city that I think is a positive one is that we’re one city and that we need a mayor who sees the city as one,” she said. The thinly veiled reference was to Mr. Ferrer’s campaign theme of “Two New Yorks” from 2001.

Mr. Ferrer’s campaign spokeswoman, Jennifer Bluestein, did not return several requests for comment for this story.

Though Ms. Segarra downplayed her relationship with Mr. Ferrer, the two have similar backgrounds. Both came from working-class families, became youth activists, and went to New York University. She went to the more radical downtown campus and he went to the uptown campus, now Bronx Community College.

Their careers have likewise been intertwined. In 1986, for example, Ms. Segarra worked on the Assembly campaign of Roberto Ramirez, then an insurgent Puerto Rican candidate who was taking on an incumbent, Gloria Davis. He lost, but four years later, backed by the Bronx machine, Mr. Ramirez won the seat.

Messrs. Ferrer and Ramirez, meanwhile, have long been like brothers, and Mr. Ramirez, a former Bronx Democratic boss, is now Mr. Ferrer’s top adviser.

The president of the Institute for Puerto Rican Policy, Angelo Falcon, who was in the same Aspira movement, said he remembers being at demonstrations with both Ms. Segarra and Mr. Ferrer.

“They were both part of that generation, my generation, of activists,” he said. “Now, they are both in the same game, but they are on opposing sides.”

Though Ms. Segarra said she was “not sure sometimes what direction” Mr. Ferrer’s campaign was facing in, she did say it was significant for Puerto Rican and Latino voters to have him in the mix.