Reiterating in effect what he had told U.S. President George W. Bush in a Japan-U.S. summit earlier this month, Prime Minister Junichiro Koizumi announced on Thursday that Japanese troops now stationed in Iraq will participate in the U.S.-led multinational force following the June 30 transfer of sovereignty. To clear the way for participation, the government at Friday's Cabinet meeting updated ground rules for troop deployment.

The announcement, which came in a meeting with the heads of opposition parties and in a subsequent press conference, raises various questions. The basic one is: Given the constitutional restraints on the use of force abroad, can the Self-Defense Forces join a multinational force that presupposes the use of force?

There is also a procedural question: Is revising a Cabinet order and other operating guidelines sufficient to permit SDF participation in what is essentially a military coalition? In other words, is the inclusion of the SDF in the multinational force consistent with the aim of Japan's Iraq assistance law, which limits its humanitarian and reconstruction activities to "noncombat areas"? Unfortunately, these questions, as well as the issue of constitutionality, have not been thoroughly discussed in the Diet.

Much of the Japanese public is apparently dissatisfied that Mr. Koizumi assured Mr. Bush of SDF participation without first discussing it at home. There is also a perception that the government, in a hasty attempt to bring Japanese troops under the multinational umbrella, chose the expediency of only revising the modus operandi -- a step that does not necessarily require parliamentary action.

Previously the government had taken the position that the SDF cannot participate in a multinational force -- such as the one that was assembled at the time of the 1991 Persian Gulf War -- because it might get involved in military action. In fact, the SDF has never joined such forces before. The question is, why now?

In brief, the official answer is that Japan will continue its efforts to help rebuild Iraq within the framework of the existing law that mandates noncombat deployment. "We will limit ourselves to humanitarian and reconstruction assistance," Mr. Koizumi told the press conference. "We cannot cooperate in security activities involving the use of force. We will do only what we can do, in ways that can win public understanding."

More specifically, Japanese participation in the multinational force is premised on four guiding principles. First, troops will remain under the Japanese chain of command, not under the commander of the multinational force. Second, they will continue to operate in "noncombat areas." Third, they will concentrate on humanitarian and reconstruction activities, such as medical care and water supply. And fourth, they will not use force as part of collective security action.

In other words, there will be no basic change for the SDF because, essentially, it will continue to do what it has been doing as a noncombatant member of the U.S.-led "coalition of the willing." Simply put, the government seems to be saying that participation in the multinational force is largely for formality's sake. But many Japanese are not convinced.

The main concern is that as a member of a military coalition whose main responsibility is to maintain security, the SDF might yet get involved in operations entailing the use of force. In fact, a new U.N. Security Council resolution endorsing the multinational force says the coalition has the authority to use every means necessary to secure Iraq, where an insurgency and terrorism continue unabated more than a year after major fighting was declared over.

Contributing to the possibility of military involvement is a view that it may be unrealistic to expect the SDF -- or any member of the multinational force -- to operate strictly under its own chain of command. Under certain conditions, cooperation may be essential. What if, it is being asked, the SDF finds itself in disagreement with decisions by the commander of the multinational force? In that kind of situation, will Japan have the option of suspending SDF activities or withdrawing its troops?

The need for Japanese cooperation in the reconstruction of the war-shattered Iraq goes without saying. Most Japanese seem to take it for granted. Still, in the absence of a more credible and detailed explanation by the government, many are wondering whether the SDF's entry into the multinational force will really help rebuild the country or serve Japan's interests. It is a serious question that should be debated exhaustively not only in a special Diet hearing but also during campaigns for next month's Upper House election.