SEATTLE (Reuters) - A California man pleaded guilty on Wednesday to threatening to kill Congressman Jim McDermott in phone messages that railed against the Washington state Democrat's opposition to extending federal tax cuts.

Charles Habermann, 32, was arrested in January, four days after Congresswoman Gabrielle Giffords, a Democrat from Arizona, was gravely wounded by a gunman who opened fire on her and a crowd of bystanders in Tucson, killing six people.

While Habermann, of Palm Springs, California, had no ties to that attack, his arrest came at a period of heightened concern about threats of violence against politicians.

Habermann entered his guilty plea to a charge of threatening a federal official during a federal court hearing in Seattle, according to the U.S. Attorney's Office.

He faced a sentence of up to 10 years in prison if convicted, but prosecutors are expected instead to seek a term of 24 to 30 months in exchange for his plea.

The case stems from two profanity-laced phone messages he left on McDermott's Seattle office answering machine in December. On one call, Habermann threatened to kill McDermott, his friends and family; in the second message he vowed to hire someone to put McDermott "in the trash."

At the time, McDermott was voicing opposition to the extension of tax cuts first signed into law by former President George W. Bush, which the congressman faulted for mainly benefiting the wealthy.

Habermann's voice messages disparaged McDermott and other Democrats' position on tax cuts and unemployment insurance.

When initially questioned at his home by FBI agents, Habermann made reference to having a $3 million trust fund, according to court documents in the case. But a spokeswoman for the U.S. Attorney's Office, Emily Langlie, said she could not verify whether the trust fund claim were true.

A two-year tax cut extension ultimately was approved by Congress and signed into law by President Barack Obama.

In 2010, Habermann was issued a warning citation by the California Highway Patrol for making threats against a member of the California state Assembly.

(Writing and reporting by Alex Dobuzinskis; additional reporting by Laura L. Myers; Editing by Steve Gorman and Peter Bohan)