WASHINGTON  An Internet radio host known for his incendiary views was arrested Wednesday in North Bergen, N.J., after federal officials charged that his angry postings about a gun case in Chicago amounted to death threats against three judges.

In a case that tests the limits of free speech, the Justice Department charged that the radio host, Hal Turner, had crossed the line into hate speech.

Mr. Turner, regarded by civil rights monitoring groups as a white supremacist, an anti-Semite and a “maestro of radio hate,” posted commentaries on his blog denouncing a ruling by the United States Court of Appeals for the Seventh Circuit, in Chicago, that upheld two local bans on handguns.

“Let me be the first to say this plainly: These judges deserve to be killed,” Mr. Turner wrote in a blog entry on June 2. “Their blood will replenish the tree of liberty. A small price to pay to assure freedom for millions.”