Apple (AAPL) announced Tuesday that it had filed a lawsuit against HTC, the Taiwanese maker of smartphones, for allegedly infringing on 20 Apple patents related to the iPhone’s user interface, underlying architecture and hardware.

“We can sit by and watch competitors steal our patented inventions, or we can do something about it. We’ve decided to do something about it,” said Steve Jobs in a statement prepared for release. “We think competition is healthy, but competitors should create their own original technology, not steal ours.”

Apple COO Tim Cook had made similar statements last year when asked about the operating system of the Palm (PALM) Pre, which bears a close resemblance to the iPhone’s. Google (GOOG)‘s Android operating system, which uses some touchscreen gestures Palm’s does not, may be even more vulnerable in a patent suit.

Google wasn’t mentioned in Apple’s press release, but the Android OS and several Android phones are named in the complaints (see below).

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Although HTC originally made smartphones that ran Microsoft’s (MSFT) Windows Mobile operating system, it began switching to Google’s Android in 2009. HTC was the first to market an Android smartphone, the G1. It now makes more than half a dozen, including the Nexus One that Google markets.

Among smartphone manufacturers, HTC is considered one of Apple’s more aggressive competitors according to Electronista. HTC implemented multi-touch in the

Android-based Hero even before Google support it. Last month it unveiled a new smartphone, the Legend, with a unibody aluminum design and black inserts that looks an awful lot like the original iPhone

The lawsuit was filed concurrently with the U.S. International Trade Commission and in U.S. District Court in Delaware. The complete court filings are available via Digital Daily here.

UPDATE: Having read the complaints, it seems clear to me that the real target is Google’s Android. Android is named in the Delaware suit (“certain mobile communication devices including cellular phones and smart phones, including at least (sic) phones incorporating the Android Operating System”). And the ITC complaint cites several Android phones by name, including the Nexus One, Magic/myTouch 3G, Dream/G1, Hero and Droid Eris.

Furthermore, the patents cited are largely if not entirely software-related, including the omnibus ‘949’ Patent — “Touch Screen Device, Method, And Graphical User Interface For Determining Commands By Applying Heuristics” — whose lead author is Steve Jobs. See Apple awarded iPhone patent.

See also:

• Apple vs. HTC: What the experts say
• Why Google’s CEO had to leave Apple’s board
• How Apple and Google compete
• Apple vs. Palm: Fresh shots across the bow
• Apple to Palm Pre: Drop dead
• Apple vs. Palm: Geeks with Grudges

[Follow Philip Elmer-DeWitt on Twitter @philiped]