ALBANY – A Manhattan lawyer, Edward Cox, vowed to press forward in his pursuit of the Republican nomination to challenge Senator Clinton’s reelection bid next year, despite the entrance of another Republican challenger with greater name recognition and apparently wider party support.

One day after the district attorney of Westchester County, Jeanine Pirro, officially began her campaign against Mrs. Clinton, Mr. Cox, whose wife is President Nixon’s daughter Tricia, launched a campaign of his own against Mrs. Pirro, calling her unprepared for the high-stakes race and saying Governor Pataki privately told him earlier this year that he was the more qualified candidate.

“The governor called me and said there are only two credible candidates in this race – you and Jeanine Pirro,” Mr. Cox said before meeting with a number of Republican county chairmen for a strategy session outside Albany yesterday. “He said you’re the best qualified candidate to run for U.S. Senate.”

Mr. Cox seized on two gaffes by the Pirro campaign during its kick-off tour Wednesday as proof that Mrs. Pirro is not experienced enough to campaign against the seasoned Mrs. Clinton. Mrs. Pirro had to stop for 32 seconds during a speech at the Waldorf-Astoria hotel in New York City because a page was missing from her speech and had to stop while delivering the same speech in Albany because of microphone problems.

“I don’t know if you can be prepared when you’ve only had one-and-a-half or two days of preparation,” Mr. Cox said of the mishaps, which were also the subject of a video parody posted on the Democratic State Committee’s Web site yesterday. The video featured Mrs. Pirro standing speechless at the podium to the theme music from a television game show, “Jeopardy.”

Mr. Cox has tried to make a campaign issue of his having spent months piecing together a strategy, while Mrs. Pirro announced her decision to run for Senate only this week. Mr. Cox’s strategy has included securing a prominent Republican fund-raiser, Cathy Blaney, and a prominent Republican pollster, Fred Steeper.

Despite Mr. Cox’s preparations, however, he has had a difficult time convincing the Republican leadership to back his candidacy. The chairman of the party, Stephen Minarik, joined 45 of 62 county chairmen in a June letter urging Mrs. Pirro to enter the race, and Mr. Minarik still publicly supports Mrs. Pirro as his personal favorite.

In addition to his charge of inexperience, Mr. Cox raised doubts about whether Mrs. Pirro will be able to raise enough money to challenge Mrs. Clinton. His advisers said funds for the Republican nominee will probably come from donors outside New York who are unwilling to send money to someone as liberal on social issues, including gun control, gay rights, and abortion, as Mrs. Pirro is.

Mrs. Pirro came under fire from abortion rights groups this week when she said she opposes a procedure known as partial-birth abortion. The group Naral Pro-Choice America said Mrs. Pirro received a 100% score on a candidate questionnaire it sent her in 2001 that included a question on whether limitations on the procedure should be allowed, suggesting that she then did not want the procedure banned.

Meanwhile, Mr. Cox came under some criticism of his own yesterday, from a former mayor of Yonkers, John Spencer, who is also seeking the Republican nomination for the race against Mrs. Clinton. Mr. Spencer predicted on the Albany-area radio station WROW-AM that he will win the Conservative Party line over Mr. Cox.

Mr. Cox said he is confident he will win the Conservative endorsement, which he called “crucial” to winning the race. No Republican has won a statewide race in New York without Conservative backing since the mid-1970s.

Mrs. Pirro’s advisers did little to counter Mr. Cox’s criticisms, sweeping in and out of yesterday’s meeting without taking questions. By contrast, Mr. Cox, and other potential candidates for statewide office who attended the event, mixed easily with reporters. The meeting was the second of several gatherings of party leaders that Republican candidates will be invited to attend in the run-up to next year’s elections.

A spokesman for Mrs. Pirro, Michael McKeon, declined to respond to several of Mr. Cox’s charges. Asked if the two mishaps Wednesday suggested a lack of sophistication, he replied, “Pass.” Asked if Mrs. Pirro’s position on partial birth abortion should be viewed as a flip-flop, Mr. McKeon said the same.

Mr. McKeon also passed on questions about how Mrs. Pirro is paying for her campaign events and on whether he is concerned about Mr. Cox’s statement that Mr. Pataki described him as more qualified. Mr. McKeon did respond to a question about whether Mrs. Pirro expects to win Conservative support.

“She’s run with Conservative Party endorsement four times,” he said, “and we expect to get it again.”

When asked by a reporter after leaving the closed-door meeting for a response to Mr. Cox’s claim that switching positions on an abortion issues is “political suicide,” Mrs. Pirro said, against Mr. McKeon’s protests, “My position has always been clear.”