The race to fill a vacant Assembly seat representing the Upper West Side is headed for a showdown Sunday, when the members of the Democratic county committee meet to pick a candidate to run in a special election at the end of February.

The seat in the 67th District opened up when Scott Stringer assumed the Manhattan presidency on January 1. Seven candidates are vying to replace him in a campaign that is pitting leaders in the district’s three influential political clubs against one another.

The committee vote could well determine who holds the Assembly seat through 2008, as the handpicked nominee figures to take the heavily Democratic district easily. The victor in the special election, which Governor Pataki has called for February 28, would serve for the rest of the year and enjoy the advantage of incumbency heading into the race for a full two-year term this fall.

The political clubs that control virtually all of the 240 committee votes are backing different candidates, leaving the race wide open, district leaders say.

“Everyone is working the spreadsheet,” a district leader with the Park River Independent Democrats, Anne Raphael, said. Ms. Raphael’s club is pushing the candidacy of Arthur Greig, a lawyer with the county committee and an ally of the state party chairman, Herman “Denny” Farrell.

Mr. Greig and three other candidates with strong party connections are seen as the favorites heading into Sunday’s vote at the John Jay College of Criminal Justice. But district leaders and committee members are watching closely for endorsements by Mr. Stringer and Rep. Jerrold Nadler, who held the 67th Assembly seat until he was elected to Congress in 1992.

Messrs. Stringer and Nadler have yet to support any of the candidates publicly, but both are said to be quietly backing Linda Rosenthal, who has directed Mr. Nadler’s Manhattan district office for more than a decade.

“In all likelihood, if she gets that backing, she will be the candidate,” a district leader, who asked not to be named, said.

Mr. Nadler declined to comment on the race, and a spokesman for Mr. Stringer said the borough president has not made an endorsement “at this time.”

“Like others on the county committee, he remains optimistic that by Monday, Democrats will be united behind a strong candidate for the seat,” the spokesman, Eric Pugatch, said.

Ms. Rosenthal is running out of what historically has been the district’s most powerful club, the Community Free Democrats, which sent Messrs. Nadler and Stringer to the Assembly. Yet she is facing strong opposition within the group from one of its district leaders, Marc Landis. Another district leader with the Community Free Democrats, Beth Berns, said she is backing Mr. Landis and that he has majority support within the club. “I’ve known him for many years, and he’s consistently helped the residents of the Upper West Side,” Ms. Berns said.

In an interview yesterday, Mr. Landis, a longtime lawyer and community activist in the district, said he is “working very hard” heading into Sunday. “I’m calling everyone for support,” he said.

Still, Ms. Rosenthal’s camp does not seem worried by Mr. Landis’s challenge. “We’re confident about how things are going to go on Sunday,” a top aide, Tom Berman, said.

The third club, the Ansonia Independent Democrats, is supporting yet another candidate: its president, Charles Imohiosen.

“He’s been an effective president, and we feel he could carry on the work of Scott,” a district leader with the Ansonia club, Phyllis Gunther, said.

District leaders said the vote would likely go to several ballots, with each candidate needing to reach a threshold of 10% or 20% to advance past the first round. Committee officials will meet with the candidates this week to determine the rules for Sunday’s vote, the county committee chairman, Tim Gay, said.

As the seven candidates jockey for the support of party leaders, different campaign strategies are emerging. The three contenders without major support within the political clubs – Charles Simon, Tom Weiss, and Michael Lupinacci – are busy collecting signatures with the hope of securing the 1,500 needed to get on the ballot if they lose the committee vote. The petitions are due on Monday, but Mr. Gay said candidates would likely contest one other’s petitions. The official ballot won’t be announced until February 10, he said.

Mr. Simon is a former deputy associate attorney general in the Justice Department and the son-in-law of a former NBC News anchor, Tom Brokaw. He said he is focused on getting on the ballot and is aggressively fund-raising with an eye toward running in the Democratic primary in September if he does not win in the special election. Mr. Simon has about $175,000 in cash on hand, he said.

Though Mr. Simon said he respects the committee voting process, he said

he would stay in the race past Sunday to give all Upper West Side Democrats a say in the election. Still, he said, “my top priority is getting the nomination through the Democratic County Committee.”

Mr. Weiss is the son of the late Ted Weiss, who preceded Mr. Nadler in Congress until his death shortly before the Democratic primary in 1992. A former journalist and strong supporter of Israel, Mr. Weiss said he has a large Jewish base of support. He is focusing on the special election in February, saying the incumbent would have a “tremendous advantage” in the race for a full term this fall.

Another candidate, Mr. Lupinacci, is a former city schoolteacher and principal running on an education platform. With little chance of winning over the committee on Sunday, Mr. Lupinacci said he is collecting signatures and is “confident” he will get on the ballot through the petition route.