NEW YORK -- Two days after announcing plans to hire 8,000 new police officers, Mayor David N. Dinkins (D) yesterday ordered a freeze on city hiring and promotions and was considering 15,000 layoffs, the most since 1975 when 25,000 city workers were laid off at the height of the city's fiscal crisis.

He said the freeze would save $115 million during this fiscal year and the next one.

Mayoral spokesman Leland T. Jones said Dinkins ordered Budget Director Philip Michael to devise a plan for layoffs to determine what impact they would have on city services. Dinkins said the recommended layoffs and other reductions would cut $800 million from an expected fiscal 1992 budget deficit of $1.4 billion.

"He's inclined to do it," Jones said.

Comptroller Elizabeth Holtzman, meanwhile, said the budget gap for next year could reach $2.6 billion. She also projected a budget deficit in the current fiscal year of as much as $738 million. Dinkins says the budget is balanced for this fiscal year.

Holtzman called for a summit of the city's top fiscal officers, labor leaders and academic and financial experts to deal with the problem.

On Tuesday, Dinkins announced a $1.8 billion crime-fighting plan that included hiring nearly 8,000 police officers.