Barnes & Noble, making a long-awaited international push, will sell its Nook e-readers and e-books in Britain for the first time beginning in October, the company said Monday.

The move will help Barnes & Noble compete with Amazon in the expanding e-book marketplace in Britain. E-book adoption there has lagged behind that in the United States, but is quickly growing, and publishing executives see it as a major opportunity for sales.

But Barnes & Noble is a late arrival to international expansion. The bookseller has long focused on building its presence in the United States even as rivals like Amazon and Apple have looked abroad. Amazon has had a presence in Britain for years, and in May the company made an agreement with Waterstones to sell the Kindle e-reader in its chain of 300 stores. Barnes & Noble had been widely expected to be the retailer to make a deal with Waterstones.

On Monday, Barnes & Noble said it would reveal partnerships with ‘‘leading retailers’’ in Britain at a later time.

Barnes & Noble has hinted for months that it would expand into Britain, but has been spare with details of when it would happen.

The Nook store, at nook.co.uk, will initially have more than 2.5 million books, magazines, and newspapers. Barnes & Noble will first offer for sale its black-and-white e-readers — the Nook Simple Touch and Nook Simple Touch with GlowLight, an e-reader with a backlighted screen that went on sale in April — but not the Nook color tablets.

Last week, Barnes & Noble trimmed prices on its tablets, lowering the price of the 16 gigabyte Nook Tablet to $199 from $249, and the Nook Color to $149 from $169. It is expected to introduce another new tablet in the fall.