Barnes & NobleShares are up more than 15% in pre-market trading after Leonard Riggio disclosed in an SEC filing this morning that he plans to make an offer for the retailer’s main business. Barnes & Noble‘s founder, chairman and largest stockholder, with nearly 30% of the voting shares, says he’s interested in the stores and barnesandnoble.com, but not the NOOK Media operation where B&N owns about 78.2% of equity along with Microsoft which has 16.8% and Pearson with 5%. Riggio’s proposal would “facilitate the Company’s evaluation of its previously announced review of strategic options for the separation of its investment in NOOK Media,” he says. The purchase price “would be negotiated with the Board” and its advisers and “is currently contemplated” to include cash and assumption of debt. Riggio would include his equity and take on the debt needed to make the deal. The company has turned the negotiations over to Patricia Higgins, who’ll chair a Strategic Committee that also includes two other independent directors: David Golden and David Wilson. They’ve already picked Evercore Partners to be their financial adviser and Paul, Weiss, Rifkind, Wharton & Garrison as legal adviser. There’s no timetable and there’s “no assurance that the review of Mr. Riggio’s proposal…will result in a sale of the retail business or in any other transaction,” the company says. B&N adds that it “does not intend to comment further” on the matter “unless and until definitive agreements for a transaction are entered into or the Strategic Committee determines to conclude the process.” Don’t be surprised, though, if analysts raise some questions about the offer Thursday, when B&N discloses its earnings for the three months ending in January. The company has already said that the NOOK unit fell short of its expectations.