A major Wall Street rating agency is upgrading New York’s bond rating, offering a vote of confidence in Mayor Bloomberg’s stewardship of the city’s budget and tangible evidence of how far New York has recovered since the 1970s, when it nearly went bankrupt.

For the third time in two years, the bond rating agency Standard & Poor’s upgraded New York City’s general obligation bond rating. Yesterday’s upgrade brought the rating up one notch to AA, the third-highest rating available and what officials said was a record high for the city.

The rating, which will allow for slightly lower interest rates on billions of dollars of debt, and potentially save the city millions, comes in response to the solid fiscal position of the city, where a soaring real estate industry and record Wall Street bonuses have opened the door for multibillion-dollar budget surpluses. New York City has spent the past three decades climbing the bond-rating ladder from the very bottom, public finance experts say, recovering from a time when the city was swimming in debt, and hemorrhaging its middle class and wealthy residents in what seemed like a vicious cycle that could only end in bankruptcy.

In a statement, Mayor Bloomberg said the upgrade “is further evidence that that our prudent fiscal planning is paying off and that New York City’s economy continues to grow.” He sounded a note of caution, however, about projected budget gaps in coming years. The city estimated a fiscal year surplus of $4.4 billion in its most recent projection, and the mayor has allocated hundreds of millions toward paying down debt.

Many of the factors contributing to the upgraded rating — the record budget surpluses; the hundreds of millions being stowed away for future retiree benefits — are the same issues that have led many on the City Council to call for tax breaks.

Council Member James Oddo, a Republican, said he wants to see the city return a reasonable amount of its surplus to taxpayers, a move that he said would maintain the city’s strong fiscal position that led to the rating upgrade.

“You can do that as long as you’re being prudent with the rest of the surplus,” Mr. Oddo said. “The bottom line is prudent fiscal policy equals higher bond ratings.”

A professor at New York University who studies public finance, Dall Forsythe, said the lower interest rates from a single increased bond rating are modest, though given the $30-plus billion in outstanding debt, the savings can add up.

The factors leading to the new bond rating offer a stark contrast with the mid-1970s, Mr. Forsythe said, when the city’s economic footing was so poor it had no bond rating at all. “The city from 1978 on — from Ed Koch on — has done a terrific job of managing its finances, and this is the reward,” he said.

In a phone interview, Mayor Koch recalled that when he came into office, he walked over to the bond rating giant Moody’s and persuaded the company to once again give the city a rating.

“We did a terrific selling job,” he said. “When I came in, the city had no bond rating, we had a $6 billion short term debt — the city had no money with which to pay.”

According to a professor at Cornell University, Martin Shefter, who wrote a book on the city’s financial woes in the 1970s, the crisis came as a result of a confluence of factors, most notably the attempts by the Lindsay and Beame administrations to rely on debt to finance daily operations as tax receipts fell.

“They responded to the political pressures of the day without realizing that that was just perpetuating the downward spiral of the city,” Mr. Shefter said.

While the route of fiscal stability has not been a straight linear path upward since the days of Mr. Koch, the trajectory has been undoubtedly positive, Mr. Shefter said, with noticeable gains in past 10 to 15 years.

A professor at Cooper Union who wrote a book on Mayor Giuliani, Fred Siegel, said it’s difficult to compare today’s situation to the 1970s, when negative national economic forces were tremendous. “In the 70s, we just lost half a million jobs — we’re not there,” he said.

While the higher bond rating reflects confidence in the city’s ability to make returns on debt, Mr. Siegel cautioned that many aspects of the city’s current fiscal situation are unstable, especially the significant growth in spending and reliance on debt during Mr. Bloomberg’s tenure.

“If we get into big deficits down the road, it will be a large measure, because Bloomberg made no serious attempt to control spending,” he said.

According to a director in the public finance department at Standard & Poor’s, Robin Prunty, New York City’s rating is slightly higher than the average municipality though lower than some of its global competitors. The company lists a rating of AA- for Chicago, AA for Boston, AA+ for London and AAA for Paris.

The bond rating agency Moody’s lists its rating for the city’s general obligations bonds as A1, the equivalent of an A+, which is two grades below AA. Fitch, the other major rating agency, lists an A+ rating for the city.