The building boom that has fed Manhattan parents’ ramped-up demand for increased school options has gained steam in 2008, widening the gap the city would have to plug to make school supply meet the estimated need, according to a report scheduled for release Friday by the president of Manhattan.

Scott Stringer will release the report with the support of the city teachers union, the speaker of the City Council, and the city comptroller. They are making the announcement at P.S. 191, a West Side elementary school they handpicked because its backdrop is a cityscape of cranes and scaffolding — under-construction high-rises that Mr. Stringer’s office said could soon lead to a flood of new students there.

The union and Mr. Stringer are also launching a campaign Saturday designed to urge the city to build more school construction funds into its next capital plan, a first draft of which is due in November.

“People have to know just how serious the situation is,” Mr. Stringer said in an interview yesterday. “But it’s with the idea that the more information we put out there, the more we can wrestle with this in the face of severe economic times.”

He said he worries the city’s tax base is at stake. “The moment that parents think that their child will not have a school seat, parents have made it clear: They will pack up and move immediately,” he said.

A spokeswoman for the city’s Department of Education, Marge Feinberg, said the city is closely monitoring residential growth in Manhattan. She named five building projects that will be completed by 2010.

Still, it is not clear that the number of seats the city is planning to create will be enough to satisfy the demand outlined in Mr. Stringer’s report. In a recent letter to elected officials about school construction plans in an area known as District 2, which encompasses much of Manhattan, school officials said they have plans to create 3,000 new seats by 2010 and almost 2,500 seats by 2014.

Mr. Stringer’s report estimates that Manhattan schools are already at a deficit of about 4,000 seats, and that the new deficit created so far in 2008 is as much as 1,100.

The figures are based on the number of residential building permits the city hands out. So far in 2008, that number is 6,600, compared with an average of about 5,000 in past years.

The city uses building permit figures to estimate how many spots will be needed in public elementary and middle schools. Mr. Stringer’s office used the same formula to reach its 1,100 estimate.

Four parts of Manhattan constitute the bulk of the boom: Chelsea and Hell’s Kitchen; Lower Manhattan; Midtown, and the Upper West Side.

The president of the teachers union, Randi Weingarten, said she sees the space crunch as a potential opportunity. Because Mayor Bloomberg controls the schools in close collaboration with the Department of Education, the city’s economic development department could work closely with the department to meet the need.

“This is the opportunity of a lifetime right now,” Ms. Weingarten said.