The cap that restricts the amount of new office space that can be approved in San Francisco would be temporarily relaxed to allow a wave of office development South of Market, under a ballot measure the affordable housing group Todco and the urban think tank SPUR submitted Wednesday.

Called the “Central SoMa affordable housing and balanced neighborhood initiative,” the measure would loosen the office space approval cap that was established in 1986, when San Francisco voters passed Proposition M, which capped new office space approvals at 875,000 square feet a year.

Though the cap has not been an issue most years — the bank of space accumulates during periods of slow development — it is a potential stumbling block to the city’s efforts to upzone Central SoMa, a 17-block area that stretches from Folsom Street on the north to Townsend Street on the south and from Second Street west to Sixth Street.

With the Central SoMa plan expected to be approved by the Board of Supervisors next year, property owners in the area have proposed 5.5 million square feet of new office construction. That’s more than double the current space — about 2 million square feet — available under Prop. M.

Todco Executive Director John Elberling said allowing those large office projects to go forward would fast-track the community benefits and fees that add up to to about $2 billion, including $900 million in affordable housing, $500 million in transit improvements, $180 million in subsidized industrial space, $160 million in park and recreational facilities, and $130 million in street improvements.

The ballot measure also would require all development fees to be paid when a project is approved, not when the building permit is pulled, which can be years later.

With the current restraints of the Prop. M space cap it could take eight years for all of the proposed office projects to win approval, according to Elberling, delaying an “extraordinary combination of community assets and benefits.”

“The bottom line is we are making an unprecedented compromise with the developers that resolves the consequences of Prop. M that would delay Central SoMa for many years in exchange for an unprecedented array of community benefits,” he said.

All the increased office space that would be borrowed from the Prop. M bank would be paid back over the next 10 years, “so there will be no overall increase in the city’s office development,” Elberling said. “It’s the borrow-and-pay-back scenario.”

Though the progressive Elberling and the business-friendly SPUR are often on the opposite sides of land-use fights, SPUR Executive Director Gabriel Metcalf called the measure “a good opportunity for the city.”

“This is a big opportunity to do something meaningful both for jobs and for housing,” Metcalf said.

The various Central SoMa benefits include three affordable housing sites, a new public swimming pool, two new public parks and the $25 million renovation of the Gene Friend Recreation Center on Sixth Street.

In addition, the ballot measure seeks to ensure that development in Central SoMa has a balance of housing and office space. Beyond an initial 6 million square feet of office space in the plan, the city could not approve any more office space until 15,000 housing units are approved.

The proposed measure was submitted to the city attorney on Wednesday for a 15-day review. After that is completed, proponents have until Feb. 5 to gather the 18,970 signatures needed to place the measure on the June 5 ballot.

A spokesperson for Mayor Ed Lee said he has not taken a position on the Prop. M initiative “but is always encouraged by any measure that accelerates the building of more affordable housing and incentivizes smart economic growth.”

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com Twitter: @sfjkdineen