NEW YORK (AP) _ Mayor Edward I. Koch's personal chef is under investigation for allegedly operating a private catering business with cars, workers, food, linen and utensils owned by the city, according to a report published today.

The New York Post said that Mitchel London, the chef at the mayor's residence, has been the subject of a probe by the city's Department of Investigation since April 26.

London is believed to have used city supplies, such as plastic forks, escargot shells and mushrooms, for his food service, the Post said.

The newspaper said Koch approved the investigation after his counsel, Pat Mulhearn, told him a former city employee had reported that 34-year-old London was using city assets to run his business.

London, who earns $49,000 a year, is the only full-time resident of Gracie Mansion other than Koch, and has worked for the mayor since 1981.

The Post said London confirmed his firm is under investigation, but said the allegations made him ''chuckle.''

London's financial disclosure forms for last year say he earned more than $1,000 but less than $5,000 in outside income from his catering firm.

London said he has spent $50,000 to $70,000 trying to build the business.

Asked if he had ever stolen city food, London said, ''I make my own purchases, I have my own people, I have my own saute pan 3/8''