Much of the US effort in Iraq in recent months has been aimed at stopping the inflow of foreign jihadis. US warplanes have blown up bridges to deny insurgent infiltration routes, troops have occupied small towns thought to be crossing points for foreigners into bigger cities, and spy drones continuously buzz the Syrian border.
Even if the US can seal Iraq's borders, stopping the flow of foreign fighters would do little to eliminate most of the country's insurgents. Only 4 to 10 percent of the country's combatants are foreign fighters, according to a report from the Center for Strategic and International Studies released last week. But while they are a minority, says the report, they are a potent segment largely from Algeria and Syria.
"The fact that there are 3,000 foreign fighters in Iraq is cause for alarm, particularly because they play so large a role in the most violent bombings and in the efforts to provoke a major and intense civil war,'' write coauthors Anthony Cordesman, a former director of defense intelligence assessment for the secretary of Defense, and Nawaf Obaid, a Saudi national and security analyst. Based mostly on Saudi intelligence, they estimate that active members of the insurgency number about 30,000.
Since the fall of Saddam Hussein, the report says, Iraq has become one of the global centers for the recruiting and training of what Mr. Cordesman and Mr. Obaid term "neo-Salafi" terrorists. These are essentially Islamist fighters that share Al Qaeda's extreme rejection of non-Muslim "infidels" and seek to create Islamic states patterned after the Arabian peninsula of the 7th and 8th centuries.
Also, the large numbers of foreign fighters who may survive the conflict are likely to return to Saudi Arabia, Egypt, and Algeria carrying terrorism skills and highly radicalized world views with them, they write.
"They are also a threat because they give bin Laden and other neo-Salafi extremist movements publicity and credibility among the angry and alienated in the Islamic world, and because many are likely to survive and be the source of violence,'' in other countries.
Most of Iraq's fighters, they say, are Sunni Arab "nationalists" who distrust Shiites now in power. Foreign fighters, the report claims, are seeking to manipulate this distrust into a wider civil war.
The authors also point out that the "fly paper" theory about the Iraq war - that a limited global number of Islamic militants would be lured to Iraq and destroyed - is probably incorrect. Instead, they estimate that many of the foreigners fighting in Iraq were peaceful before the US invasion.
In particular, the authors find that the presence of Saudi militants in Iraq has been overstated - estimating they make up 1 to 2 percent of fighters there - but say that most of the young Saudis fighting in Iraq were not violent before the war.
One of their paper's "primary conclusions is the unsettling realization that the vast majority of Saudi militants who have entered Iraq were not terrorist sympathizers before the war; and were radicalized almost exclusively by the coalition invasion."
Relying on interviews with US and Saudi intelligence officials, as well as the findings of the Saudi National Security Assessment Project, which is directed by Obaid and is described as a private group, the paper says that Algerians make up the largest group of foreign fighters at 20 percent, followed by Syrians (18 percent), Yemenis (17 percent), Sudanese (15 percent) and Egyptians (13 percent).
Because Turkey and Iran are less hospitable to foreign extremists, and the Saudi border is a well-patrolled harsh desert, Syria has been the principal means of entry for foreign fighters into Iraq.
Syria's 380-mile border with Iraq is well traveled and porous. In a guide for would-be Jihadis posted on Internet forums, a "Mujahidin" who calls himself Al Muhaijar al-Islami, urges brothers to make the crossing along the Syria-Anbar Province border in Eastern Iraq, according to a translation of the document provided by Evan Kohlman, a New York-based terrorism consultant.
Al Islami says "close connections" among Sunni Arab tribes - like the Shamar who live on both sides of the border and whose influence stretches into Saudi Arabia - make passage easier, as does their disdain for the central Syrian government.
He says the large number of scattered villages there, and frequent engagements with US forces in cities like Al Qaim, make it possible to walk into Iraq in 30 minutes.
He warns militants to shave their beards, carry cigarettes (most Salafis don't smoke), and avoid shortening their robes after the fashion of Salafis.
Cordesman and Obaid's findings seem to back up Al Islami's advice. They point out that 270,000 Saudis visited Syria alone in the first half of this year.
"Separating the legitimate visitors from the militants is nearly impossible," they write. "The problem of successfully halting the traffic of Saudis through Syria into Iraq is overwhelmingly difficult, politically charged, and operationally challenging."
In the end, while they're worried about the potential for foreign fighters to spread terrorism and violence to their homelands once they leave Iraq, they argue that pacifying the country is now far from a simple counter-insurgency operation.
"The outcome in Iraq is going to be determined by how well Iraq's political process can find an inclusive solution to bringing Arab Sunnis, Arab Shiites, Kurds, and Iraqi minorities into a state that all are willing to support,'' they write. "Military action, counterinsurgency and counterterrorism cannot unite or build a country."
• To read the entire CSIS report go to www.csis.org/press/wf_2005_0919.pdf.