Washington (CNN) -- The terrorist threat to the U.S. homeland has continued to "evolve" and may now "be at its most heightened state" since the September 11, 2001, terror attacks, Homeland Security Secretary Janet Napolitano told members of Congress on Wednesday.

The most significant risk to the United States is probably posed by al Qaeda in the Arabian Peninsula and Anwar al-Awlaki, said Michael Leiter, the director of the National Counterterrorism Center. The American-born Muslim cleric has close ties to al Qaeda, and has been linked to Army Maj. Nidal Hassan, the alleged culprit behind the November 2009 shootings at Fort Hood, Texas.

There is an increased reliance on recruiting Westerners into terrorist organizations, Napolitano said during testimony before the House Homeland Security Committee. State and local law enforcement officers are increasingly needed to combat terror, and a greater focus is needed on aiding law enforcement to help secure communities, she said.

Along with the joint terror task force led by the FBI, the nation's four-pronged counterterrorism response includes locally run "fusion centers" aimed at facilitating intelligence-sharing and analysis; a nationwide reporting initiative for suspicious acts; and the "If you see something, say something" campaign designed to "foster public vigilance," Napolitano added.

The campaign has been rolled out at major public events such as the Super Bowl and at retail centers, Napolitano said.

In addition, as previously announced, authorities are replacing the color-coded terror alert system with a more useful one, she said. The new system will reflect the nation's need to be ready while also keeping the public as informed as possible, she said.

Al Qaeda is at its weakest point in the last decade, but remains "a very determined enemy," Leitner said, noting there have been multiple disrupted plots in northern Europe in the last five years.

Authorities are also watching groups such as the one behind the 2008 attacks in Mumbai, India, Lashkar-e-Tayyiba; Hezbollah; and Greek anarchists like the ones thought to have sent letter bombs to embassies.

At the same time, "homegrown radicalization is a growing threat, and one we cannot ignore," said New York GOP Rep. Peter King, the committee's chairman.

The attacks at Fort Hood show that attacks from radicals within the United States do not need to be sophisticated to be effective, Leiter responded.

Rep. Paul Broun, R-Georgia, used the hearing to argue that Transportation Security Adminstration employees should be actively profiling Muslims at airports, as opposed to randomly selecting people in security lines.

"We're not focusing on those people who want to harm us, and the people who want to harm us are not grandmas," Broun said. "Give me a break. ... We've got to profile these folks."

Napolitano argued that terrorists would ultimately benefit if certain airport screening procedures do not remain random. If rules are set down regarding the treatment of certain groups, she said, terrorists would "know those rules" and learn how to manipulate them.

Asked about congressional deliberations over whether to extend key provisions of the Patriot Act, Leiter said the measure remains "a very important tool" for law enforcement officials, particularly in terms of stopping domestic extremists. It would be "very problematic" if the provisions are allowed to expire, as currently scheduled, at the end of February, he said.

Among other things, the provisions allow for roving wiretap surveillance of certain targets without requiring law enforcement officers to constantly seek new court orders.

The House voted 277-148 on Tuesday in favor of extending the provisions through early December, falling 13 votes shy of the two-thirds majority required for passage.