By DAVID ESPO
AP Special Correspondent
WASHINGTON (AP) -- Rep. Gabrielle Giffords of Arizona announced Sunday she intends to resign from Congress this week to concentrate on recovering from wounds suffered in an assassination attempt a little more than a year ago that shook the country.
"I don't remember much from that horrible day, but I will never forget the trust you placed in me to be your voice," the Democratic lawmaker said on a video posted without prior notice on her Facebook page.
"I'm getting better. Every day my spirit is high," she said. "I have more work to do on my recovery. So to do what's best for Arizona, I will step down this week."
Giffords was shot in the head and grievously wounded last January as she was meeting with constituents outside a supermarket in Tucson, Ariz. Her progress had seemed remarkable, to the point that she was able to walk dramatically into the House chamber last August to cast a vote.
Her shooting prompted an agonizing national debate about super-charged rhetoric in political campaigns, although the man charged in the shooting later turned out to be mentally ill.
In Washington, members of Congress were told to pay more attention to their physical security. Legislation was introduced to ban high-capacity ammunition clips, although it never advanced.
Under state law, Arizona Gov. Jan Brewer must call a special election to fill out the remainder of Giffords' term, which ends at the end of 2012.
President Barack Obama on Sunday called Giffords "the very best of what public service should be."
"Gabby's cheerful presence will be missed in Washington," Obama said. "But she will remain an inspiration to all whose lives she touched - myself included. And I'm confident that we haven't seen the last of this extraordinary American."
House Speaker John Boehner, R-Ohio, said he saluted Giffords "for her service and for the courage and perseverance she has shown in the face of tragedy. She will be missed."
In a statement, House Democratic leader Nancy Pelosi of California said that "since the tragic events one year ago, Gabby has been an inspiring symbol of determination and courage to millions of Americans."
Democratic officials had held out hope for months that the congresswoman might recover sufficiently to run for re-election or even become a candidate to replace retiring Republican Sen. Jon Kyl.
The shooting on Jan. 8, 2011, left six people dead, a federal judge and a Giffords aide among them. Twelve others were wounded.
A 23-year-old man, Jared Lee Loughner, has pleaded not guilty to 49 charges in the shooting. He has been diagnosed with bipolar disorder, and is being forcibly medicated at a Missouri prison facility in an effort by authorities to make him mentally ready for trial.
In the months since she was shot, Giffords, 41, has been treated in Houston as well as Arizona as she re-learned how to walk and speak.
She made a dramatic appearance on the House floor Aug. 2, when she unexpectedly walked in to vote for an increase in the debt limit. Lawmakers from both parties cheered her presence, and she was enveloped in hugs.
More recently, she participated in an observance of the anniversary of the shooting in Arizona.
In "Gabby: A Story of Courage and Hope," a book released last year that she wrote with her husband, the astronaut Mark Kelly, she spoke of how much she wanted to get better, regain what she lost and return to Congress.
She delivers the last chapter in her own voice, saying in a single page of short sentences and phrases that everything she does reminds her of that horrible day and that she was grateful to survive.
"I will get stronger. I will return," she wrote.
Giffords was shot in the left side of the brain, the part that controls speech and communication.
Kelly commanded the space shuttle Endeavour on its last mission in May. She watched the launch from Cape Canaveral, Fla.
Kelly, who became a NASA astronaut in 1996 and made four trips into space aboard the space shuttle, retired in October.
© 2012 The Associated Press.