The stock of Marvel Entertainment Group Inc. dropped to a 52-week low Friday, after Spider-Man’s owner said it expects robust growth, but not until the second half of the year.Even so, the comic book publisher and entertainment company said 1994 earnings will be well above last year’s levels. Marvel’s stock fell $ 2 to $ 19 in New York Stock Exchange trading. “Publishing will be soft in the first half after a bout of speculation-fueled growth in the comic book market in 1993, but should improve in the second half as the market resumes more rational growth and we launch most of our major publishing programs,” Terry Stewart, Marvel president and chief operating officer, said in a statement. The revenue boost in the second half will come from promotions tied to summer , back-to-school, Halloween and Christmas programs. And the company expects a bump in licensing sales from the fall premiere of “Spider-Man TV” and the “Marvel Action Hour” starring Iron Man and the Fantastic Four, both on Fox. Number crunching Marvel said it agreed with Wall Street analysts’ estimates of 1994 earnings of 74 cents to 78 cents a share, up from 55 cents a share a year ago. But that will break down into 11 cents-12 cents in the first quarter; 12 cents-13 cents in the second quarter; 25 cents-26 cents in the third quarter; and 26 cents-27 cents in the fourth quarter. The news led Salomon Brothers Inc. to downgrade its recommendation on Marvel to “hold” from “buy.” Marvel’s products include Spider-Man and other comic books, Fleer trading cards and Double Bubble gum.