Milken Highest-Paid Wall Streeter: Indicted financier Michael Milken was the highest-paid Wall Street professional in 1988, earning more than $180 million as "junk bond" chieftain for Drexel Burnham Lambert, according to estimates compiled by Financial World magazine. Milken was one of two executives in the top 10--along with Singer Co. Chairman Paul A. Bilzerian--indicted or convicted this year for securities laws violations. Gordon Cain, chairman of the petrochemical concern Sterling Group, was second with $120 million. No. 3 was Henry Kravis, partner in the leveraged buyout firm Kohlberg Kravis Roberts & Co., who earned "at least" $110 million. Bilzerian, who was convicted June 9 for securities fraud, was sixth on the list with estimated earnings of at least $80 million last year.