It depends on how you define threat

I suspect that the FBI has been smoking a little of what the DEA has been impounding.

In a recent Senate briefing John Lewis, the FBI's deputy assistant director for counterterrorism, confirmed that ALF and ELF are the real terror threats to our nation. They have accounted for over 1,200 illegal acts since 1990 and the count has been rising. At the same time, the number of incidents involving right wing groups, the KKK, the National Alliance, American Nazi, the various anti abortion groups and other right wing groups have been in decline.

But, here is where I think a failure in understanding on the part of the FBI comes in.

No deaths have been blamed on attacks by those groups so far, but the attacks have increased in frequency and size

This is an important fact to note, and in fact defines these two sets of terror groups. ALF and it better known cousin ELF are terror groups, but there actions in the past do indicate a strong desire to avoid the risk to human life. When you consider the actions of those on the right, the reverse seems to be the case.

Alan Berg is gunned down, or 50 Hummers are destroyed; a homemade weapon of mass destruction in Texas or a fire at a unoccupied ski resort: ALF released 200 lab animals and 2 militia wacks did this.

Notice a pattern?

Both groups are involved in crime, terrorism, and neither deserves our support. One group appears to select it actions to cause economic harm to a limited sector of the society, the other seems to be focused on killing people.

Now notice who the government has decided is the bigger threat.