A federal judge in Washington held a reporter for Time magazine in contempt of court yesterday and ordered him jailed for refusing to name the government officials who disclosed the identity of undercover CIA operative Valerie Plame to him. The magazine was also held in contempt and ordered to pay a fine of $1,000 a day. The judge, Thomas Hogan, suspended both sanctions while Time and its reporter, Matthew Cooper, pursued an appeal. But the judge firmly rejected their contention that the First Amendment entitled journalists to refuse to answer a grand jury”s questions about confidential sources. Legal experts said yesterday that the potential jailing of a journalist represented perhaps the most significant clash between federal prosecutors and the news media since the 1970”s. The case is one of several making their way through federal courts in which journalists have been ordered to reveal their sources. Like Cooper, Tim Russert, of NBC”s “Meet the Press,” received a subpoena in May. But unlike Cooper, Russert agreed to cooperate. In a statement, NBC said Mr. Russert was interviewed under oath by prosecutors on Saturday. A Washington Post reporter, Glenn Kessler, was interviewed by prosecutors in June. A second Post reporter, Walter Pincus, said he received a subpoena yesterday.