Experts and government officials say 2009 could be the most dangerous year in terms of domestic terror threats since 2001.

The scale, number and variety of terror plots with ties to the United States detected this year is alarming, particularly those that involve American citizens accused of conspiring with al-Qaida.

Because American Muslims tend to be wealthier, have higher levels of education and are better integrated, it was generally believed fewer would develop or act on radical beliefs. That appears to be changing.

Army Maj. Nidal Malik Hasan, accused of killing 13 people at Fort Hood, may have had emotional problems, but radicalized Muslim beliefs may also be a motive, authorities have said. Hasan has been linked to Anwar al-Awlaki, a former imam who is alleged to be an al-Qaida recruiter. Hasan and three of the 9/11 hijackers have attended al-Awlaki's sermons.

This past week, a Chicago man was charged with conducting surveillance on potential targets in Mumbai prior to terrorist attacks in the Indian city in 2008.

David Coleman Headley, an American citizen, also is charged in plotting the attack of a newspaper in Denmark, which published 12 cartoons in 2005 that depicted the Prophet Muhammad. This triggered protests in parts of the Islamic world.

The arrests of Americans conspiring with al-Qaida and the discovery of their terror plots speak to the diligence of law enforcers and cooperation among international authorities.

But an increased number of arrests of American-born Muslims or Muslims who are naturalized citizens suspected of plotting terror attacks or supporting radical terror groups suggests that young Muslims may be as prone to radicalization as Muslims in Europe. Militants may be more driven by a quest for identity and a need to bond with like-thinking people than personal hardship.

To that end, some American Muslims are traveling abroad for terror training or to plot attacks. Some return to the United States to plan domestic attacks.

Najibullah Zazi, for instance, traveled to Pakistan in 2008 to plot one of the most serious terrorist attacks in the United States since Sept. 11, 2001. Zazi, 24, is an Afghan immigrant who worked as an airport shuttle driver in Denver. He allegedly scoured area beauty supply stores to purchase chemicals needed to build bombs for al-Qaida. He and fellow suspect Bryant Neal Vinas, 26, reportedly met in Pakistan in 2008 to discuss attacks on various American targets such as New York subways and trains. Zazi and Vinas are the first Americans accused of joining al-Qaida in several years.

These cases illustrate the evolving nature of the domestic terrorist movement. Opposing these elements will require information-sharing on the part of international authorities and a willingness of everyday Americans to report suspicious activity.