A building boom is driving the number of construction jobs to record high numbers, taking the number of people employed in the sector to 130,000 in 2009, up from 116,000 in 2006, a new study says.

The new jobs come even as residential construction is expected to decline over the next two years, according to the report by the New York Building Congress, dropping to an expected 30,000 units in 2009 from an estimated 35,000 units in 2007.

Despite the projected decline in residential construction, the Building Congress expects a host of large commercial and infrastructure projects to lift spending to all-time highs, projecting spending on construction of more than $29 billion in 2009, up from a record high $24.6 billion in 2006.

Publicly funded infrastructure improvements such as the Second Avenue Subway, the no. 7 line extension, and the third water aqueduct account for thousands of jobs and billions of dollars.

Taken with the possible construction of four professional sporting arenas and stadiums, at least 12 million square feet of development at the West Side rail yards, five towers at the World Trade Center, and numerous other large and small projects around the city, New Yorkers can expect to see even more cranes and cement trucks.

“All boroughs of the city are doing very, very well,” the president of the Building Congress, Richard Anderson, said at a breakfast hosted by the advocacy organization. “The outlook is quite strong for this year, and the next two years will be at least at inflation.” The number of construction jobs expected next year, 126,700, would surpass the previous record of 124,800 set in 2001.

On the management side, some industry leaders are concerned that the especially high demand for positions such as project managers and superintendents could set back the timelines on construction projects, as not enough people can be found to fill the jobs.

“Projects could be delayed if the strength of this market continues and the acceleration of schedules continues,” the CEO of the Building Trades Employers’ Association, Louis Coletti, said. “The construction industry has not been on the top of the list of engineering students.”

While the outlook from the Building Congress was generally positive, Mayor Bloomberg yesterday warned of a possible economic slowdown in the city, saying the number of “big real estate transactions has come to a screeching halt,” slowing tax receipts.

“While I don’t think we’re going to have a recession in this city, I think it’s probably true that we will have a slowdown in economic activity,” Mr. Bloomberg told reporters. “I think you can expect real estate prices to fall.”