Welcome to Harry Potter and the Marketing Blitz. Scholastic Inc. is launching one of the largest publicity campaigns in the publisher’s history in support of the June 21 release of Harry Potter and the Order of the Phoenix, which itself will have an initial printing of 8.5 million copies. The company is spending between $3 million and $4 million on the campaign. Marketing plans for the book, the fifth in the series, include advertising on an electronic billboard in Times Square; ‘‘Harry Potter’’ — themed days at four Major League Baseball games, during which fans will be encouraged to dress up as characters from the series; and promotional items, such as mini-bumper stickers and buttons, to be given away at retail stores, many of which are planning midnight parties on the day of the book’s release. ‘‘This is probably our biggest single launch,’’ said Jennifer Pasanen, vice president of marketing for Scholastic. After becoming a success in Britain — where the series’ author, J.K. Rowling, resides — Scholastic published the first three books in the US in 1999, then co-ordinated a worldwide release of the fourth title in July 2000. In the three years since that book was published, two big-budget movies, based on the first two titles, have been released. The series’ core readership of pre- and early teens has aged, too (although, as Pasanen points out, Harry himself is 15 in the new book). To reach those former 13-year-olds who are now 16, Pasanen said Scholastic is branching out from Nickelodeon- and Disney-related media and into more mainstream fare in order to reach older teens. Although Scholastic is relying on the success of the book — it’s expected to contribute 5-6 percent of the company’s annual sales — others are, too. The title went to the top spot of Amazon’s best-seller list two hours after the online retailer made it available for pre-orders in January, and it has been there ever since. Although it hasn’t released the number of current pre-orders, about 350,000 people ordered the fourth book from Amazon before its release. ‘‘Hundreds of thousands’’ already have ordered the book from Barnes & Noble.com, the online retailer of the book chain, said spokeswoman Carolyn Brown. ‘‘We expect it to to be the best-selling book that we’ve ever had,’’ she said. (LAT-WP)