* Doctors say congresswoman, shot in head, is responsive
* Suspect charged with five counts in U.S. court
* Police find text referring to "assassination"
* Shooting sparks concerns about political rhetoric (Adds timing of hearing; refiles to fix time conversions)
By Tim Gaynor and Peter Henderson
TUCSON, Ariz., Jan 9 (Reuters) - The U.S. government on Sunday charged a 22-year-old man with attempted assassination in the Arizona shooting rampage and doctors expressed optimism that congresswoman Gabrielle Giffords, who was shot in the head, would recover.
The shooting of Giffords and 19 other people -- six of whom were killed -- in Tucson on Saturday fueled debate about extreme political rhetoric in the United States after an acrimonious campaign for congressional elections in November.
The U.S. government charged Jared Lee Loughner with two counts of first degree murder, one count of attempted assassination of a member of Congress and two other counts of attempted murder. Prosecutors said other charges could be filed.
Loughner was due to appear in court in Phoenix at 2 p.m. MST (4 p.m. EST, 2100 GMT) on Monday, the Justice Department said, [ID:nN09215739], as reports emerged of a troubled man who had been asked to leave a local college for disruptive behavior.
Investigators said in the charges they found an envelope at his residence with the handwritten phrases "I planned ahead" and "My assassination," along with the name "Giffords" and what appeared to be Loughner's signature.
The suspect opened fire with a semi-automatic Glock pistol at close range while the Democratic congresswoman was attending a political meeting in a supermarket parking lot. U.S. federal judge John Roll and a 9-year-old girl were among the six people killed. Fourteen people were wounded.
Full coverage of the Giffords shooting [ID:nN0899911]
Story on political rhetoric [ID:nN09198081]
FBI Director Robert Mueller told a news conference public officials should be on alert, but there was no information to suggest a further specific threat. Mueller said "hate speech and other inciteful speech" presented a challenge to law enforcement officials, especially when it resulted in "lone wolves" undertaking attacks.
President Barack Obama called on Americans to observe a moment of silence on Monday at 11 a.m. EST (1600 GMT) to commemorate the victims of the shooting.
Giffords, a 40-year-old Democrat, was in critical condition but was able to follow simple commands, such as holding up two fingers when asked, doctors at University Medical Center in Tucson said. [ID:nN09215739]
A single bullet traveled the length of her brain on the left side, hitting an area that controls speech. Given the devastating wound, doctors said they were uncertain about the extent of brain damage she may have suffered.
Giffords has been put into a pharmaceutical coma but was being awakened frequently to check her progress.
"There are obvious areas of our brain that are less tolerant to intrusion," said Dr. Michael Lemole. "I don't want to go down the speculation road but at the same time we're cautiously optimistic."
Gun violence is common in the United States but political shootings are rare.
Pima County Sheriff Clarence Dupnik said a wounded woman, identified by CNN as Patricia Maisch, had grabbed away an ammunition magazine from the gunman as he tried to reload after shooting into the crowd. He managed to fit in another magazine but it jammed and he was tackled by two men.
The violence shocked politicians in Washington. Some Democrats said a climate of political vitriol might have played a role. "We are in a dark place in this country right now and the atmospheric condition is toxic," Democratic Representative Emanuel Cleaver told NBC's "Meet the Press" program.
But Jon Kyl, a Republican senator from Arizona, cautioned against a "rush to speculate."
"We really don't know what motivated this young person, except to know he was very mentally unstable," Kyl said on the "Face the Nation" show on CBS.
The father of the slain 9-year-old girl said she was born on September 11, 2001 -- the day of the hijacked plane attacks on New York and Washington. "She came into the world on 9/11 and then at 9 years old she leaves it all on this terrible day,"