NEW YORK -- Dun & Bradstreet Corp. and IMS International Inc. announced yesterday an agreement under which IMS would be merged into the information and publishing company in a stock swap valued at $1.77 billion.

Under the agreement approved by the companies' boards of directors, each of IMS' 41.7 million outstanding shares would be exchanged for 0.801 share of Dun & Bradstreet, or a total of approximately 33.4 million Dun & Bradstreet shares.

Dun & Bradstreet stock closed at $53 Friday on the New York Stock Exchange, while IMS stock finished at $30.62 1/2 on the over-the-counter market.

IMS also granted Dun & Bradstreet an option to purchase under certain, unspecified circumstances 6.26 million shares, or about 15 percent, of IMS' outstanding common stock for $42.45 a share in cash or shares of Dun & Bradstreet.

The merger, announced in a joint statement by Dun & Bradstreet and IMS, is subject to the approval of shareholders of both firms and to the expiration of waiting periods under federal antitrust laws.

IMS' businesses include market research and publishing in the health care industry. Dun & Bradstreet's information and publishing segments include Donnelly Directory, Moody's Investors Service and Nielsen Marketing Research and Media Research.