“The Last of the Mohicans” has emerged as this fall’s surprise box office standout with adept marketing from studio 20th Century Fox. But observers say the key is the quality of the film itself and the lack of strong competition, at least to date.But “Mohicans’ ” hot streak could end this weekend. The film that’s been No. 1 on the charts for the past two weekends will face what movie marketing exex view as its first major challenge in the form of Warner Bros.’ action pic “Under Siege” starring Steven Seagal. “Mohicans” has held up well in the face of “Hero” (Columbia), “The Mighty Ducks” (Disney) and “Mr. Baseball” (Universal), but how will it fare against a heavily backed movie whose star has a devoted following? “If you take a look at what’s been in the marketplace, there hasn’t been a big film out there,” noted movie marketing consultant David Forbes. Sources say Warner will back “Under Siege” heavily–with total media spending in the range of $ 9 million to $ 10 million. The film, starring Seagal as a sailor battling terrorists, opens wide tomorrow on 2,042 screens. Observers expect the Seagal film to open big–perhaps with an initial box office take as high as $ 15 million–if it follows the pattern of Seagal’s other films. Fox marketing prez Andrea Jaffe thinks the next two weekends will be “Mohicans” big test. She acknowledges that the Michael Mann film may experience a “dip” this weekend because of “Under Siege.” Last weekend “Mohicans’ ” business fell off only 12% after it opened at No. 1 with $ 10,976,661 on 1,491 screens. Industry speculation placed Fox’s initial ad spending on “Mohicans” at $ 15 million, but Jaffe dismisses such figures as the jealous grousing of rivals whose films did not hold up in the face of “Mohicans.” Such reports are “silly,” she said, adding that if a studio spent that kind of coin to open a film it wouldn’t make any money. Jaffe said she appreciates the compliments Fox’s marketing program has gained with “Mohicans,” but she acknowledges much of the success stems from the movie itself. “It’s always the product,” she said. $ 60 to $ 65 mil haul Jaffe expects that the film will eventually generate $ 60 million to $ 65 million at the box office during its theatrical run. The success of “Mohicans” is somewhat surprising considering the studio changed its release date from summer to fall–a move that usually signals trouble for a film. Jaffe said the studio made the change after previewing “Mohicans.” Fox decided the movie was more of a fall film because of its more serious tone–beyond the popcorn action flicks that dominate the summer box office. In addition, the studio felt “Mohicans” had Oscar potential, so a fall release would help in that regard. Fox’s Jaffe said the film’s target audience is equally divided among males and females, ages 21 and up. Initial media buys included heavy expenditures in sports programming. Print ads show off the critical raves the film has garnered with positive quotes and feature a western-clad Daniel Day-Lewis running, tomahawk in hand. Despite the domestic launch-date reshuffling, the pic’s overseas distributor, Morgan Creek Intl., decided to proceed with its planned European opening as scheduled. “Mohicans” opened in France on Aug. 26, followed by Norway and Sweden this past weekend. It will roll out in the United Kingdom Nov. 6, in Spain Dec. 4, in Germany Jan. 14 and in Japan in March. A hard sell Observers are impressed by “Mohicans’ ” performance considering it’s a period piece. Marketing mavens consider such films hard to sell by nature. In addition, “Mohicans’ ” star, Daniel Day-Lewis, was a wild card: While the Oscar winner is considered a consummate actor, he has not been a major box office draw, at least so far. “Mohicans” must rate as his first truly commercial film. Day-Lewis’ agent, Gene Parseghian, said his “Mohicans” role “enhances the perception of him as a chameleon.” Day-Lewis’ next movie is also a period piece, but it will be an entirely different setting and tone. He will be the lead in Martin Scorsese’s film “The Age of Innocence,” based on the Edith Wharton novel. Columbia will release it in fall 1993. Like “Mohicans,” the release date was changed, when Columbia opted to delay its planned Dec. 25 release to next fall to allow the director more time to edit the film.