MARKETING SERVICE FIRMS produced a record $4.8 billion in strategic deals in the last half of 1998, according to Winterberry Group Inc., a Manorville, NY investment banking firm. There were 188 mergers, acquisitions and investment transactions-104 in the last quarter alone. Teleservices companies topped the roster in terms of dollar volume, producing 19 deals with a value of $1.4 billion. General agencies were next, with 42 deals worth $1.2 billion. Though database companies produced only 16 transactions, these generated $423.4 million. Direct response agencies conducted 28 deals valued at $417 million. Promotional service companies weighed in with 12 deals totaling $422 million. The industry percentages were similar in the fourth quarter, for which a total transaction volume of $2.6 billion was reported.