It's only a matter of time before Al Qaeda (search) or other terrorist groups try to launch an attack on the United States with chemical, biological or nuclear weapons, CIA Director Porter Goss (search) told a Senate panel on Wednesday.

Al Qaeda is trying very hard to circumvent U.S. security and launch an attack on U.S. soil, he said, adding that they are getting their training on the urban battlefields in Iraq.

"Islamic extremists are exploiting the Iraqi conflict to recruit new anti-U.S. jihadists," Goss told the Senate Intelligence Committee. "Those jihadists (search) who survive will leave Iraq experienced in and focused on acts of urban terrorism. They represent a potential pool of contacts to build transnational terrorist cells, groups and networks in Saudi Arabia, Jordan and other countries."

Elsewhere on Capitol Hill, Defense Secretary Donald H. Rumsfeld (search) told the House Armed Services Committee that he believes terrorists are regrouping for another strike. In defending his $419 billion 2006 fiscal year budget request, Rumsfeld said the United States is preparing to deal with any threat.

"The extremists continue to plot to attack again. They are at this moment recalibrating and reorganizing. And so are we," the Pentagon chief said.

Appearing at the committee with Goss, FBI Director Robert Mueller (search) added that he is not just worried about terrorists abroad. He said radicalized Muslim converts in the United States are doing their best to go undetected.

"First is the threat from covert Al Qaeda operatives inside the U.S. who have the intention to facilitate or conduct an attack. Finding them is a top priority for the FBI, but it is also one of the most difficult challenges. The very nature of a covert operative trained not to raise suspicion and to appear benign is what makes their detection so difficult," Mueller said.

"We are continuously adapting our methods to reflect newly-received intelligence and to ensure we are as proactive and as targeted as we can be in detecting their presence," he said.

More than three years have passed since the Sept. 11, 2001, terror attacks on the World Trade Center and Pentagon, and while intelligence officials say homeland security has improved, the resolve of these groups has grown over time. The most-wanted terrorist in Iraq, Abu Musab al-Zarqawi (search), for instance, hopes to establish Iraq as a safe-haven to bring about a final victory over the West, Goss said.

Vice Adm. Lowell Jacoby, head of the Defense Intelligence Agency, said political reform movements in Iran have faltered and that country continues to support terrorism and aid insurgents in Iraq.

In fact, among the largest threats highlighted in the hearing is the one from Iran, which the agency chiefs warned wants to damage American interests in the Middle East.

Under questioning from panel members, Goss said Tehran is trying to keep up with neighbors like Pakistan, which has nuclear weapons already. He said Iran's intent is to suggest to neighbors that it has equal capabilities. But that level of "ambiguity," added Carl Rodney, principal deputy assistant secretary of state for intelligence and research, makes it difficult to analyze Iran's capabilities because of it suggestive remarks.

Pakistan was able to obtain nuclear weapons through the work of Pakistani scientist A.Q. Khan (search), who is currently being questioned by Pakistani authorities about how much of the information he had was shared with other nations. Goss said that the intelligence community has yet to get to the "end of the trail" of the nuclear black market run by Khan.

Because of his role in dealing arms, Khan has left open the door that organizations as well as states could obtain nuclear, chemical or biological weapons.

The threat from nuclear weapons that may be missing from Russia also is unknown, Goss told senators, saying that enough material is "unaccounted for" that someone with the right know-how could make a nuclear device. He could not say who may be in control of that material.

"I can't account for some of the material so I can't make the assurance about its whereabouts," he said.

Goss and Mueller also defended themselves from criticism that has plagued the intelligence community since the Sept. 11 attacks and follow-up inquiry by the commission designed to point out the agencies' flaws. In December, Congress passed a bill to help the agencies sort out their messes and to create a director of national intelligence to oversee communications and gathering techniques.

Ranking Democrat Jay Rockefeller said "it is unacceptable" that a director of national intelligence has still not been put in place. He said whoever takes the job will be "at a distinct disadvantage."

President Bush has yet to name a nominee for the job though some officials indicated recently that a name could be offered soon. On top of that, next month, Bush's commission to investigate the intelligence community's capabilities on weapons of mass destruction (search) is also expected to submit its findings.

Given the after-the-fact investigations into the Iraq intelligence, Senate Intelligence Chairman Pat Roberts (search), R-Kan., said his panel will become more proactive in how it reviews the intelligence community's strengths and weaknesses, already focusing on nuclear terrorism and Iran.

FOX News Catherine Herridge and Julie Asher and The Associated Press contributed to this report.