WASHINGTON — Hackers believed to be operating from China have broken into computers in Congress, apparently in search of information on Chinese dissidents, two Republican lawmakers said yesterday.

The hackers were not identified, but one of the lawmakers, Rep. Chris Smith of New Jersey, a senior Republican on the House Foreign Affairs Committee, said he believed that all signs pointed to the Chinese government.

Federal authorities have been increasingly concerned in recent years about the Chinese government’s aggressive deployment of scientists, engineers, foreign businessmen, students, and others to sweep up American technology and information. Protecting the America against cyber-based attacks and high-tech crimes is the FBI’s third investigative priority behind combating terrorism and public corruption.

The extent of the intrusions on Capitol Hill, which officials said began in August 2006, was unclear, although Rep. Frank Wolf, a Republican of Virginia, whose office had four computers affected, said that other members of Congress were targeted as well as at least one congressional committee. “They got everything,” Mr. Wolf said at a press briefing describing the attack on his office systems.

Mr. Wolf said that following one of the attacks, a car with license plates belonging to Chinese officials went to the home of a Chinese dissident in the Washington suburbs and took photographs of it.

The Chinese government had no immediate comment on the allegations.

Mr. Wolf said an FBI probe confirmed the hacking incidents. The bureau declined comment.

The hacking report is the latest example of the vulnerabilities of private and public institutions to possible espionage and other crimes. Countries have been using cyber espionage for years to access valuable information in America, and China has made no secret of its interest in information warfare.

“Congress would be an attractive target for any spy or hacker, especially if there was information on political dissidents and on U.S. policies,” a senior fellow and technology program director at the Center for Strategic and International Studies in Washington, James Lewis, said. Mr. Lewis said while China may be a logical suspect, good hackers are adept at hiding their tracks.

“We have a very sophisticated set of opponents. It could be the Chinese. It could be the Russians. It could be somebody else,” he said. “This isn’t an amateur’s game anymore. Particularly when you are talking about an interesting target like a congressman’s human rights files, the folks who are going after that are not going to be teenagers in Mendocino.”