State Senator Olga Mendez has four offices in her district, but she conducts most of her business on the telephone from her East Harlem apartment, where she has lived by herself since her husband’s death in 1970. “She’s always on the phone with somebody,” her chief of staff, Federico Colon, said. “Even when I’m trying to have a meeting with her about something important, she can’t stop picking up the phone.”

The senator surrounds herself with a protective ring of aides, one of them her nephew, but whenever any question arises, no matter how inconsequential, it has to be floated past the senator first.

One day last week she left her apartment for a campaigning event at a Spanish senior center in East Harlem. The breakfast crowd didn’t seem particularly excited when she stepped into the room, but that was before the 79-year-old made like a stray kitten and hugged and kissed and rubbed up against every soul in the room.

At one point Ms. Mendez found herself facing Pat Flanagan, a disheveled man whose long beard was as amorphous and unruly as sea foam. She looked momentarily confused before reaching out and raking her fingers through the facial hair. “She has sparks!” Mr. Flanagan wowed after she’d moved on to pet somebody else. “She’s like Eva Peron. She has a palpable sexual energy!”

The 28th State Senate district is made up of East Yorkville, Roosevelt Island, East Harlem, and the South Bronx. It is said to be the poorest district in the state. A month after the last time she was re-elected, Ms. Mendez switched from the Democratic to the Republican Party, a move that prompted a 32-year-old Democrat on the City Council, Jose M. Serrano, son of Rep. Jose E. Serrano of the Bronx, to run against her.

In 26 years, this is the first time Ms. Mendez has faced a serious challenger. The Republicans hold 37 seats to 24 for the Democrats in the state Senate, but the gap stands to narrow this year, given how many Republican incumbents are facing fearsome opposition. “It’s a change of pace,” Mr. Colon said early on a recent Sunday morning. He looked a little worried, and rubbed his eyelids.

Convincing a population that votes Democratic 10 to 1 to send a Republican to Albany will take more than the usual mailings and dated photographs in bodega windows. Ms. Mendez has some major explaining to do. She insists her beliefs remain the same as ever, and her political conversion is simply the means to win her district more funds from a Republican-controlled state Senate. “I am still my own boat,” she insisted, adding she estimates her switch has given her constituency access to five times the money she could have obtained as a Democrat. “I don’t have a fiber of Republican in me. I’ve always been a goddamn liberal!”

But she’s also quick to malign the Democratic Party: “The Democrats never gave me money, never sent me bodies, never defended my petitions. Never.”

The Republican Campaign Committee has given the Mendez campaign at least $224,150. “They supported me,” she said. “The only thing the Democrats wanted was to get rid of me.” Mr. Serrano has received $15,000 from the Democratic Campaign Committee.

The senator’s relationship with the Republican Party is a curious one. She refrained from attending the Republican National Convention this summer because she said she’s not a Republican, and yet she was always a strong Giuliani supporter, and she’s supporting President Bush’s re-election over Senator Kerry. “I am a very intuitive person,” she said. “I get very bad vibes from Kerry. It’s something I can’t explain. It sounds ridiculous.”

At the senior center, many of those present appeared to be thinking about matters that had nothing to do with politics – getting extra servings of fruit was a popular pursuit that morning. Yet the senator gave it her all. A little under the weather, she had to take occasional pauses to cough, but she never tired of pointing, yelling, and stamping her feet with brio. When she was done she smoothed over her purple pantsuit and said, “Gracias. ?Me van a aplaudir?” and the seniors followed her instructions, clapping for the energetic lady with the big blond curls.

“I had such a good time,” she said on the telephone that afternoon. “I had so many people tell me I was beautiful. Tell me something – do I look my age?”

Told that she doesn’t, and that her skin looked so plump to the point of seeming airbrushed, she said: “Let me tell you something. So many times I fall asleep without taking off my make-up. They say that’s the worst thing you can do. Ha!” Her laughter made her start to cough again.

Olga Mendez grew up in Puerto Rico, in a well-to-do family with seven other children. By her accounts she was a quick student, and skipped second grade, fourth grade, and sixth grade. She came to New York to go to get a graduate degree in psychology at Columbia, and she stayed on, working as a psychology researcher and marrying a man named Rafael Perez.

“I was madly in love,” she said, “but he just wanted to play golf all day.” He also took to drinking and gambling, she recalled, and Ms. Mendez told him he had three strikes and he was out. “He wouldn’t fool around with women, but I don’t care. I was miserable in other areas,” she said. “Marriage can be a damn terrible thing.”

Five years into the marriage, she walked, and she didn’t remarry until she was in her thirties, when she met Tony Mendez, of the Mendez political machine. His father, Anthony, was Tammany Hall’s top ally in East Harlem. One night several years into their marriage, Tony Mendez’s dead body was left outside their apartment building. He had a head wound and an autopsy later revealed he had been asphyxiated. “It was the most traumatic experience,” she said. “I said, ‘I’m never going to go through this horrible pain’ – and I was a good looker. I said, ‘No more dates.'”

Two years later she ran to be a Mc-Govern delegate at the Democratic National Convention, and her career in politics took off. She went on to become district leader, and by 1978 she had a seat in the Senate. She claims she’s never been beholden to any party and was always “independent.” Indeed, her campaign literature contains the word “Independent” and fails to mention she’s the Republican candidate. A recent visit to one of her campaign offices, whose sign reads “Democrats for Olga Mendez,” found a volunteer who insisted the senator was a Democrat. When a colleague of hers explained that actually the senator had switched party alliances, the woman said, “Well, she’s a Democrat at heart.”

On the issues, Ms. Mendez and Mr. Serrano see some things differently, but all told they’re more alike than not. They’re both for affordable housing, raising the minimum wage to $7.15 an hour, bringing in money for education, and easing the Rockefeller drug laws. He’s in favor of gay marriages; she draws the line at civil unions.

Come November 2, many voters will vote strictly along party lines, but there will also be a fair share of those who feel that their 26-year-old history with Ms. Mendez can’t be rent by labels. She has become a fireball of an icon, while Mr. Serrano is known for being soft-spoken, often reluctant to put on his schmooze hat. “When he’s campaigning people often don’t realize he’s the candidate,” one insider said. “They’re like, ‘Why is this guy shaking my hand?'”

Just before letting me off the phone the other day, Ms. Mendez said, “Let me tell you one thing.” She recalled something Tony used to tell her: “You’re so fortunate you were born a woman. If you were born a man, the things you say, somebody would have hit you in the jaw by now.”

She had already told me this story, word for word, but her laughter was so depraved and salty it sounded fresh.