Can the four-day Memorial Day frame – which in recent years has become the biggest weekend at the box office – support three blockbusters? “Star Wars: Episode III – Revenge of the Sith,” which rang up $108.4 million during last week’s three-day span, is expected to retain its box office crown for Fox over the holiday. Though they’re both expected to open strongly, the weekend’s newcomers are in a close fight for second place: Paramount’s “The Longest Yard,” bowing in 3,634 theaters, and DreamWorks’ “Madagascar,” going out ultra-wide at 4,131. However, even if all three movies perform as well as expected, industry observers expect the total biz over four days to be lower than that of the year-earlier frame. Over the holiday in 2004, the combination of “Shrek 2’s” second-week total of $95.6 million and “The Day After Tomorrow’s” $85.8 million debut lifted the weekend total to a mighty $247.8 million. Even if the frame falls short, extending to 14 weeks the streak in which this year’s weekend totals have been lower than 2004, the strong midweek grosses for “Star Wars” may continue to close the gap in year-to-date box office. In its first seven days of release, “Sith” has scored $191.4 million domestically.