WASHINGTON  Ralph D. Fertig, a 79-year-old civil rights lawyer, says he would like to help a militant Kurdish group in Turkey find peaceful ways to achieve its goals. But he fears prosecution under a law banning even benign assistance to groups said to engage in terrorism.

The Supreme Court will soon hear Mr. Fertig’s challenge to the law, in a case that pits First Amendment freedoms against the government’s efforts to combat terrorism. The case represents the court’s first encounter with the free speech and association rights of American citizens in the context of terrorism since the Sept. 11 attacks  and its first chance to test the constitutionality of a provision of the USA Patriot Act.

Opponents of the law, which bans providing “material support” to terrorist organizations, say it violates American values in ways that would have made Senator Joseph R. McCarthy blush during the witch hunts of the cold war.

The government defends the law, under which it has secured many of its terrorism convictions in the last decade, as an important tool that takes account of the slippery nature of the nation’s modern enemies.