The city is on track to post a $1 billion surplus this fiscal year, according to the Independent Budget Office. That is almost twice the figure originally projected and stands Mayor Bloomberg in better stead as other agencies have been doom-casting about the city’s financial picture.

“Should the money go back to taxpayers? Of course it should,” an analyst at the Manhattan Institute, E.J. McMahon, said. “But it won’t. The mayor still has next year’s gap to fill.”

It is that gap, forecast earlier this year to be as much as $3.7 billion, that has tempered enthusiasm about the larger-than-expected current surplus. While the Independent Budget Office predicts in a report released yesterday that the future gap may be closer to $2.3 billion, other agencies, including the Financial Control Board and the city comptroller’s office, remain concerned.

In a separate report released yesterday, the board said it projects gaps of almost $3 billion in fiscal 2006, growing to more than $4 billion in fiscal 2007. Those estimates don’t reflect any new collective-bargaining increases after fiscal 2006, or any higher awards on current contracts for uniformed services or the teachers union. Both those contracts are awaiting negotiation.

Another looming liability comes from a panel of special masters, who recommended that education spending in the city increase in the next four years to exceed current annual outlays by $5.6 billion. While city officials have welcomed that finding, it is unclear just how much of that spending increase the city will have to shoulder.

Where everyone agrees, numbers aside, is that the city’s finances are structurally unbalanced. “Revenues are constrained by a forecasted weak economic recovery and upward pressure continues on operating expenditures,” the control board said in a statement yesterday.

The Independent Budget Office, which is part of the city government but is an independent watchdog agency, agreed. “Rising expenditures for debt service, pensions, health and fringe benefits, and Medicaid continue to strain the city’s resources,” its report concluded. “Despite a projected $1 billion surplus in the current fiscal year that can be used to prepay some of next fiscal year’s expenses, the city still faces a $2.2 billion shortfall in 2006. And without a surplus generated in 2006, the gap for 2007 will be harder to close.”

The Independent Budget Office projected that the total city spending will rise at an average rate of 2.3% annually from 2005 through 2008, making it doubly difficult to balance the budget, as is required by law.