Jay L. Kriegel, who as a 25-year-old prodigy helped shape the Lindsay administration’s progressive challenge to New York City’s entrenched power brokers, and who later emerged as one himself, in fields ranging from television broadcasting to real estate development, died on Thursday at his weekend home in South Kent, Conn. He was 79.

The cause was complications of melanoma, his wife, Kathryn McAuliffe, said.

A charter member of Mayor John V. Lindsay’s so-called kiddie corps, Mr. Kriegel played an outsize role as chief of staff and special counsel in an administration that held power from 1966 to 1973. Later, as an indefatigable but pragmatic outside process broker, he continued to influence a broad spectrum of policymaking through the same power of persuasion.

His behind-the-scenes counsel, on behalf of private clients or the civic groups he volunteered to help, made him everyone’s go-to guy in navigating government bureaucracy. Recognizable in later years by his formidable gray mane, he would argue their cases, with his adenoidal inflection, at a machine-gun pace.

“Talking to Jay Kriegel,” a colleague once said, “is like putting your finger in an electric light socket.”