After writing intensely, even obsessively, for years about government surveillance and the prosecution of journalists, Glenn Greenwald has suddenly put himself directly at the intersection of those two issues, and perhaps in the cross hairs of federal prosecutors.

Late Wednesday, Mr. Greenwald, a lawyer and longtime blogger, published an article in the British newspaper The Guardian about the existence of a top-secret court order allowing the National Security Agency to monitor millions of telephone logs. The article, which included a link to the order, is expected to attract an investigation from the Justice Department, which has aggressively pursued leakers.

On Thursday night, he followed up with an article written with a Guardian reporter, Ewen MacAskill, that exposed an N.S.A. program, Prism, that has gathered information from the nation’s largest Internet companies going back nearly six years.

“The N.S.A. is kind of the crown jewel in government secrecy. I expect them to react even more extremely,” Mr. Greenwald said in a telephone interview. He said that he had been advised by lawyer friends that “he should be worried,” but he had decided that “what I am doing is exactly what the Constitution is about and I am not worried about it.”