The United Synagogue wants a co-ordinated approach under the leadership of Chief Rabbi Ephraim Mirvis to address the predicted shortage of places in Jewish secondary schools in north-west London.
Two applications to open a Jewish secondary free school are set to go to the Department for Education this month, although neither has so far gained the Chief Rabbi's support.
One bid is expected to come from the supporters of the Barkai College project, the other jointly from Kedem High School and the Hertfordshire Jewish Free School (HJFS) groups.
The Chief Rabbi has voiced reservations about the free school model because under current entry rules only half the places could be guaranteed to Jewish children.
Other options include relocating King Solomon High School from Essex to north London, or opening more classes at existing Jewish schools.
A US spokesman said: "A co-ordinated approach, under the auspices of the Chief Rabbi, will ensure that we are able to create the school places required efficiently and in a sustainable manner".
One source close to the interested parties said "frantic negotiations" were going on behind the scenes.
Maurice Ashkenazi-Bakes of HJPS confirmed its plan to go ahead with a joint application with Kedem, "with a view to open a school in 2017".
He said "friendly discussions" had taken place with Barkai about combining, but felt this was "unlikely to happen".
One difference of opinion is over location - Barkai favours Barnet, while the HJFS group are looking more to the Hertfordshire or Harrow area.
The option of a secondary school on the site of Hertsmere Jewish Primary School was not feasible, he said.
Dr Richard Burack, King Solomon co-chairman, said there had been no approach from the US, the school's foundation body, about relocation.
The next round of successful free school applicants is due to be announced in March.
