NEW YORK, OCT. 20 -- This city's comeback from financial ruin has been powered in large measure by the economic engine called Wall Street, and officials here are worried that the sputtering stock market could take the steam out of future growth.

The securities industry has accounted for one in four new jobs here over the last decade, even as manufacturing and many other business sectors were declining. As the bull market roared on last year, Wall Street payrolls ballooned by $2 billion, one-third of the 1986 increase in private-sector paychecks here.

"New York City's fortunes are more closely tied to the fortunes of this roller-coaster industry today than ever before," said Samuel Ehrenhalt, the Labor Department's regional commissioner of labor statistics. "The city's economy is less diversified than it was 20 years ago."

While the 157,000 jobs on Wall Street amount to less than 5 percent of the city's work force, the stock market's growth has created tens of thousands of jobs for advertising agents, lawyers, accountants, computer operators and secretaries as well as for developers who build the skyscrapers that house them.

Alair Townsend, deputy mayor for economic development, maintains that "all of our eggs are not in one basket," citing growth in such fields as construction, transportation and health care. But, she said, "If the {securities} industry gets into trouble, we'll feel it."

Mayor Edward I. Koch (D) said the market's plunge raises the possibility of service cutbacks. "We are considering the appropriate retrenchment actions," he said. "Obviously, we want to have a very diversified economy, but we're never going to get out of the service area."

Koch added: "I believe that we will never, ever be in the condition that we were in from 1975 through 1980. We know when to turn the tap off or slow it down."

The first rumblings of what Ehrenhalt called the market's "earthquake" could be heard last week when Salomon Bros., a major brokerage here, announced a 12 percent cut in its work force and hinted that it would reconsider plans to move to a controversial skyscraper planned for Columbus Circle.

Ehrenhalt said this signals a major "restructuring" in a white-collar industry. He said the local real estate market could also be hurt.

Recent history suggests cause for concern. As the stock market declined from 1969 to 1975, the number of jobs on Wall Street dropped from 105,000 to 67,000. The doubling of jobs since then has coincided with New York's rebound from near-bankruptcy.

Ehrenhalt said the nation's financial capital is in danger of losing its preeminence to London and Tokyo and to domestic competitors because new technology makes it more feasible for banks and brokerages to move support staff out of Manhattan.