NEW YORK — Martin Kraar, the top professional at the Council of Jewish Federations and one of the most powerful Jewish leaders in the country, is leaving the new CJF-United Jewish Appeal partnership.

He will take over as executive vice president of the American Committee for the Weizmann Institute of Science.

Kraar's decision to leave CJF after 10 years as its chief executive and an influential force in the partnership's creation, was both personal and professional.

"I really believe it's time for me to make a change," he said this week, adding that as CJF, UJA and the United Israel Appeal finalize their merger, one of the most important decisions they will make is to decide on a new executive.

Kraar's departure ends months of speculation about his future, but leaves open the question of who will lead the newly formed entity.

Together, CJF, UJA and UIA — which recently set up shop together in a lower-Manhattan building under the banner "UJA Federations of North America" — represent the major fund-raising organization and service provider to American Jews and Jewish communities worldwide, raising an estimated $1.4 billion a year.

Their merger will create the largest Jewish governing body in North America and for the first time will consolidate power in one office.

Kraar sent a letter to the CJF last month removing himself from the selection process.

CJF President Conrad Giles said he was saddened, but not surprised by Kraar's decision.

"I have been aware that Marty was considering other options for the past year," he said.

Kraar's recent tenure has been consumed with plans for what has been called "the road to merger."

Rumors about the position's prime candidates have circulated since plans for a CJF-UJA partnership first surfaced.

The names most often mentioned come from the top tiers of America's largest federations. They include Steven Nasatir, president of the Jewish Federation of Metropolitan Chicago; Robert Aronson, executive vice president of the Jewish Federation of Metropolitan Detroit; and Stephen Solender, executive vice president of New York's UJA-Federation.

Choosing one of them is considered a more likely scenario than giving the post to Bernard Moscovitz, executive vice president of UJA.

But another option is bringing in a high-profile individual from outside the federated system.