The company’s rivals are banding together to purchase patents to keep them out of Google’s hands and taking other steps to make it more expensive for handset makers to use the Android operating system, David Drummond, chief legal officer at Mountain View, California-based Google, said in a blog posting.

“We thought it was important to speak out and make it clear that we’re determined to preserve Android as a competitive choice for consumers, by stopping those who are trying to strangle it,” Drummond wrote. Android’s success has resulted in a “hostile, organized campaign against Android by Microsoft, Oracle, Apple and other companies, waged through bogus patents.”

Apple, Microsoft and Google have ramped up spending on patent portfolios in recent months to gain exclusive rights to a broadening array of technology, much of it used in the emerging area of smartphones. As bidding intensifies, prices for patents are surging, fueling concerns that portfolios are overvalued. Oracle sued Google last year, accusing it of patent infringement over the use of Java technology used in Android.

“This patent scramble is a land rush for leverage -- leverage over Google, for starters,” said Patrick Walravens, an analyst at JMP Securities. “The best defense in patent legislation is having a bunch of patents of your own.”

‘Patent Bubble’

A group that includes Apple and Microsoft beat out Google in June with a $4.5 billion bid for patents previously owned by Nortel Networks Corp. Rivals are “banding together” to purchase patents they in turn can use to charge fees that will make Android devices more expensive, Drummond said.

“This anti-competitive strategy is also escalating the cost of patents way beyond what they’re really worth,” Drummond wrote. “The law frowns on the accumulation of dubious patents for anti-competitive means -- which means these deals are likely to draw regulatory scrutiny, and this patent bubble will pop.”

The U.S. Justice Department is examining the Nortel deal to see whether it hurts competition in the smartphone industry, a person familiar with the matter has said. If the Justice department doesn’t challenge the transaction, the winning bidders will control more than 6,000 patents and applications that cover wireless technologies.

Steve Dowling, a spokesman for Cupertino, California-based Apple, and Deborah Hellinger, a spokeswoman for Redwood City, California-based Oracle, declined to comment. Tricia Payer, a spokeswoman for Redmond, Washington-based Microsoft, also declined to comment.