ALBANY – New York Attorney General Eliot Spitzer accused insurance executive Maurice “Hank” Greenberg yesterday of participating in a series of financial transactions 35 years ago that cost the charitable foundation of his mentor $6 billion.

Mr. Spitzer’s allegations were contained in a letter delivered yesterday to the president of the Starr Foundation. They represent the latest escalation of his battle with Mr. Greenberg, who resigned in March as the chairman and chief executive of American International Group amid widening federal and state probes of accounting irregularities at the world’s largest property and casualty insurance company.

The Starr Foundation’s 2003 tax return filed with the Internal Revenue Service listed assets of $3.6 billion, made up mostly of shares in AIG, and showed that it made more than $188 million in charitable donations that year. The bulk of those were grants to colleges and tuition payments made for students.

The attorney general urged the foundation to take civil action against Mr. Greenberg and suggested he would do so if they don’t act by the end of January to recover the assets and reconstitute its board “to guarantee it the independence needed to advance its charitable mission into the future.”

Mr. Spitzer alleged in the letter that records obtained by court order from AIG’s Bermuda offices show that three transactions in 1969 and 1970 were rife with conflicts of interest that harmed the interests of the charitable foundation.