More companies, particularly blue chips, are turning to outside suppliers for marketing help--mainly in selling to ethnic groups and other hard-to-reach consumers. Serving that niche is Snyder Communications (SNC), which designs complete marketing programs aimed at reaching ''high-value'' and fairly inaccessible customers.

Snyder's stock, after hitting a low of 20 in mid-April, rebounded to 34 on Dec. 2. Based on a 1997 earnings estimate of 46 cents a share, the stock trades at a lofty price-earnings ratio of 73. So the stock could be vulnerable in a market pullback. Nonetheless, investment pro Andrew Lanyi, who heads Lanyi Research at CIBC-Oppenheimer, thinks Snyder is on the way to 55. ''A high p-e doesn't scare me, so long as strong earnings visibility is there,'' he argues.

He thinks the company, whose database has 30 million students in the U.S. and 20 million multicultural consumers--such as Hispanics and Russians--will continue to grow fast. One client, AT&T, accounts for 20% of its business. Talks are under way to renew its contract with AT&T, which ends at yearend. ''Snyder is almost certain to get not only a renewal but a much bigger contract from AT&T,'' says Lanyi. AT&T declined comment. Other big clients: Procter & Gamble, Kellogg, and Pfizer.