One longtime political aide was upset and another cruised to victory yesterday as local Democratic leaders chose nominees to fill three vacant state Assembly seats in Manhattan and Brooklyn.

In the 74th District on Manhattan’s East Side, Sylvia Friedman, a veteran community activist, upended Steve Kaufman, the designated heir apparent of former Assemblyman Steven Sanders. Mr. Sanders retired last year after 28 years in the Assembly and quickly threw his support to Mr. Kaufman, his chief of staff.

“It was an enormous surprise,” an East Side district leader and Kaufman supporter, Charles Buchwald, said of Ms. Friedman’s victory. Ms. Friedman won in a close vote on the second ballot at a county committee meeting at the New York University Medical Center.

Ms. Friedman, a former district leader and City Council candidate, said she was “thrilled” by the nomination but not surprised.

“I knew that he thought he had it,” she said, referring to Mr. Kaufman, ” but I also knew that I had a lot of support.”

Ms. Friedman said that if elected, she would focus on health care, low-and moderate-income housing, and on securing state funding for city schools.

On the Upper West Side, Linda Rosenthal, an adviser to Rep. Jerrold Nadler, won the support of the Democratic county committee, surviving challenges from six other candidates with the help of Mr. Nadler and the man she hopes to succeed, the Manhattan president, Scott Stringer. The 67th District seat opened up when Mr. Stringer became borough president on January 1.

And in an uncontested ballot, Democrats in the 59th District in Brooklyn chose Alan Maisel as their nominee to succeed Assemblyman Frank Seddio, who resigned after his selection to be a surrogate judge. Mr. Maisel served as Mr. Seddio’s chief of staff for five years.

All three nominees are running in heavily Democratic districts and figure to be heavy favorites heading into the special election called by Governor Pataki for February 28. If elected, the candidates would also enjoy the advantage of incumbency in the election for a full two-year Assembly term this fall.

In the Upper West Side race, Ms. Rosenthal secured her win in the last several days as Messrs. Nadler and Stringer, the district’s top powerbrokers, made calls on her behalf to many of the nearly 240 county committee members. Mr. Nadler had held the 67th District seat before his election to Congress in 1992, and Ms. Rosenthal had directed his Manhattan office for the last 13 years.

Two of Ms. Rosenthal’s top challengers, Charles Imohiosen and Arthur Greig, dropped out last week, leaving behind a largely two-horse race between Ms. Rosenthal and Marc Landis, a community activist and district leader. While Ms. Rosenthal enjoyed the backing of influential party leaders, Mr. Landis ran the more aggressive campaign. At yesterday’s nominating meeting in a cafeteria at the John Jay College of Criminal Justice, Mr. Landis’s camp sponsored a refreshment table, provided each committee member with a biography and position papers, and decked the hall with posters.

Ms. Rosenthal won with 57% of the weighted vote, 20% more than Mr. Landis. Four other candidates split the remaining ballots.

The race on the Upper West Side has also pitted party insiders who came out of the district’s powerful Democratic clubs against candidates who are seeking the seat from the outside, either through aggressive fund-raising or grassroots campaigning.

A former deputy in the Justice Department, Charles Simon, has mounted an insurgent candidacy and raised more than $200,000 for the special election. Despite garnering minimal support from the county committee, Mr. Simon says he has more than the 1,500 signatures needed to get on the ballot by petition.

A district leader with the Community Free Democrats political club, Beth Burns, said Mr. Simon could make things very difficult for Ms. Rosenthal given his significant fund-raising advantage.

“Even though she’s the Democratic Party candidate, she’s going to have to raise a lot of money very quickly,” Ms. Burns said.

Mr. Stringer said Ms. Rosenthal was at an “incredible disadvantage” when it came to money, but he lent his strong support. “She is capable, she is smart, she is ready to go,” he said.

In accepting the nomination, Ms. Rosenthal said she was “deeply honored.” Seeking to unify the district’s divided factions, she told the committee, “I plan to represent all of you in this room.”

Ms. Rosenthal, in a light-hearted note, also alluded to her long service to Mr. Nadler. She said her young nephew’s first question for her was, “Who’s going to work for Jerry?”