With the prominent introduction of the phone, Samsung is trying to end its role as understudy to its more celebrated competitor, especially in the crucial American market, where Apple still rules. Even as Samsung has surpassed Apple in global market share, it is often criticized in the United States as an effective copycat, taking most of its product cues from Apple. But Samsung has begun flexing its marketing muscle more aggressively here to try to change that perception.

“This is Samsung’s time right now,” said Gene Munster, an analyst at Piper Jaffray. “They are clearly gaining more attention this time around than they ever have.”

Apple itself is showing signs of concern. In an unusual move on the eve of the Samsung event, Philip W. Schiller, Apple’s senior vice president for worldwide marketing, gave several interviews in which he discussed flaws in mobile devices based on Android, the Google operating system used by most of Samsung’s smartphones.

But Apple still has many big advantages that allow it to defend its position in the mobile business. Its iPhone 5 was the best-selling smartphone in the world in the holiday quarter, even though Samsung’s vast portfolio of phones is bigger than Apple’s. By charging a premium for its products, Apple raked in 69 percent of the profits in the smartphone business last year, compared with 34 percent for Samsung, according to a report by T. Michael Walkley, an analyst with Canaccord Genuity. (The numbers add up to more than 100 percent because Apple and Samsung combined made more money than other competitors lost.)

While analysts like Mr. Munster expect Samsung to gain market share in the United States in the coming two quarters, they predict Apple is likely to still dominate the crucial holiday shopping season, when gift shoppers buy mobile devices in droves. That is when sales of the iPhone typically outperform all other devices. By unveiling its flagship phone just before spring, Samsung is striking at Apple months before a new iPhone is expected to be released.