The planned complaint has already sparked outrage in Washington, but legal experts said it is likely to be rejected following recent changes to Belgium's war crimes law to prevent such charges against Americans.
CBS News Legal Analyst Andrew Cohen says one possible scenario is that Belgium could get the lawsuit and then promptly pass the case along to Iraq at some point and say, essentially "Here, these allegations against General Franks, true or not, and actionable or not, have nothing to do with us and everything to do with the Iraqi people. So go ahead and pursue it if you want, but we won't."
Another possibility, says Cohen, is that the Pentagon might choose to "ignore this lawsuit if it ever gets filed and essentially thumb its nose at whatever legal maneuvering the lawsuit produces. But that might create a much messier situation down the road, especially if the Belgian courts accept the case and begin to order US officials to do this or that while they are under Belgium jurisdiction. Even if those officials claim diplomatic immunity, it could get ugly."
The complaint against Franks is to be filed by attorney Jan Fermon, who is running for parliament Sunday in Belgium's national elections, representing the small, far-left Resist group.
Fermon said the complaint would also include charges against other U.S. military personnel, whom he did not identify.
Two other leftist candidates, Dr. Geert Van Moorter and Dr. Colette Moulaert, found the 16 wounded or bereaved Iraqis in whose name the complaint was lodged while working for a medical aid group in Baghdad during the war.
Belgium introduced laws in the early 1990s to authorize its courts to try genocide and other war crimes wherever they occurred. The law was first used to target suspects in Rwanda's 1994 genocide who fled to Belgium, the former colonial ruler of the central African nation.
Since then, complaints have been brought against a string of world leaders including Fidel Castro, Yasser Arafat and Saddam Hussein, although none have gone to trial.
The Belgian government rushed changes to the law through parliament last month after complaints lodged against Israeli Prime Minister Ariel Sharon, former President Bush and current U.S. Secretary of State Colin Powell soured relations with Washington and Jerusalem.
Under the new amendments, Belgian courts should refer foreigners facing war crimes charges to their own countries if they are democracies with a record of fairness in justice.
Despite that, Fermon said he was optimistic that his claim would be accepted. "We have a very specific case, with specific evidence," he said in a recent interview.
Among claims Fermon made against Franks were a failure of U.S. troops to prevent the looting of hospitals after the Saddam's fall and the alleged U.S. bombing of a crowded market in Baghdad, which Iraqi officials claimed killed more than 60 people.
A Belgian prosecutor will have to study the allegations before deciding whether a case should be opened.
Fermon's announcement last month that he planned to file the complaint provoked concern from the U.S. government.
"The Belgian government needs to be diligent in taking steps to prevent abuse of the legal system for political ends," said State Department spokesman Richard Boucher.