When heads of state of the seven most highly industrialized nations (the so-called G-7) hold an economic summit meeting in Houston next week, will they meet as seven sovereign nations each representing its own policies? Or will they meet as four units -- the United States, Japan, Canada and the European Community?

Now is the time for the United States, Japan and Canada to consider and explore with their European Community friends the impact that growing economic, social and political union will have on the various international bodies in which the several EC members sit.

Will EC members in Houston, in NATO, in the CSCE, participate as individual states, or as part of a group bound by prior consultations and decisions?

The question is important: first, because an ever-larger portion of foreign policy decisions (including decisions with important fiscal implications) is being made and implemented in multilateral arenas, and second because the decisions of such groups are often different from the decisions of their single-member states.

This is especially important to the United States because the process of compromising differences within the EC can deprive America of the support of good friends on controversial issues. The United Kingdom could never have permitted U.S. planes to overfly Britain to bomb Libya if the matter had been decided in the EC. Britain would have been bound by the EC majority that opposed the bombing.

The question of who is speaking for whom will make a real difference in Houston when West German Chancellor Helmut Kohl and French President Francois Mitterrand raise the issue of massive ($15 billion) Western aid to the Soviet Union.

Kohl, eager to remove Soviet objections to German unification, promised Mikhail Gorbachev that he would push urgent, massive aid with his Western friends. Mitterrand, eager to have German help in pushing European union, agreed to join Kohl in making the case.

The two leaders coordinated plans to serve their nations' interests by selling the proposal for Soviet aid first to the EC, then to the G-7. In Dublin, where EC heads of state met last week, a decision was made to support Soviet aid in principle but to defer decisions on specifics to the EC's October meeting. In addition, specific note was taken that Mitterrand and Kohl had inscribed the matter on the agenda of the Houston meeting.

Mitterrand and Kohl were probably satisfied with this outcome. The fact that the EC had considered the question and reached a decision constituted a large step toward a common EC foreign policy -- a goal ardently wished for by supporters of European political union.

There was every reason for the EC to defer developing specifics until there had been an opportunity to bring three big potential donors on board. There is also good reason to suppose the EC endorsement will be welcome to President Bush.

Bush has on several occasions expressed his desire to see the EC move on to greater economic, social and political union. He has readily agreed to the EC's coordinating U.S. food aid to Poland and to the EC's serving as a clearinghouse for Eastern European aid. And he acquiesced in U.S. participation as a relatively minor partner in the EC's European Bank for Reconstruction and Development, through which Mitterrand has proposed to channel Soviet aid.

Bush has a habit -- a good habit -- of coordinating initiatives with allies. And it may be that he sees the EC as facilitating coordination.

But, of course, as Mitterrand and Margaret Thatcher understand with special clarity, the medium shapes the message. Decisions made in the EC may be quite different from those of any member. A proposal for Soviet aid endorsed by the EC may inhibit the full expression of Thatcher's reservations, even though she is not easily inhibited.

Before the United States acquiesces in a binding EC voice in negotiations that include America, the implications and consequences should be carefully considered.