SAN FRANCISCO  More electronic books are coming to mobile phones.

In a move that could bolster the growing popularity of e-books, Google said Thursday that the 1.5 million public domain books it had scanned and made available free on PCs were now accessible on mobile devices like the iPhone and the T-Mobile G1.

Also Thursday, Amazon said that it was working on making the titles for its popular e-book reader, the Kindle, available on a variety of mobile phones. The company, which is expected to unveil a new version of the Kindle next week, did not say when Kindle titles would be available on mobile phones.

“We are excited to make Kindle books available on a range of mobile phones,” said Drew Herdener, a spokesman for Amazon. “We are working on that now.”

Google’s move greatly expands the number of e-books that are available for reading on the go. The Kindle currently offers about 230,000 titles.