SMARTING at Western Europe's relegation from a once-central player in the Middle East to little more than an observer in the Mideast peace conference, the European Community will offer a "peace for economic development" proposal to reassert Europe's presence in the region.The proposal, to be unveiled in the EC's address to the peace conference, draws from the Community's experience in using its regional development assistance to encourage peace in Central America, and in coordinating Western economic aid for Eastern Europe. "There can only be an effective and durable peace in the region if there is stability, and for that to exist there must be steady and equitable economic development," says an EC spokesman. The proposal points up the EC's reliance on its economic presence to counterbalance its underdeveloped political weight in the international arena. From the Gulf war to the Yugoslav crisis, the Community consistently uses its economic leverage. The EC address will be delivered during the opening session by Dutch Foreign Minister Hans van den Broeck. The Netherlands currently holds the EC's rotating six-month presidency. The EC plan will likely encourage a growing regional interdependence by sponsoring and guiding development projects, trade, and technological exchange. The regional development plan, to which the Community would serve as guarantor and coordinator, was developed by EC Commissioner Abel Matutes, who oversees existing EC aid to the Middle East. European officials appear resigned to Europe's peripheral role in the Madrid conference's three-day opening session. But Mr. Matutes advocates a dash by the EC to preside over multilateral regional development talks, if and when the conference process reaches that stage. European countries have been little more than bystanders during recent months as the United States pushed, coaxed, and cajoled Israelis and Arabs into participating in the peace conference. It was not supposed to be this way. French President Francois Mitterrand argued to the reluctant French, for example, that their military participation in the Gulf was necessary to insure France a place at the Middle East negotiating table. Aside from a delegation of journalists, the French have no marked presence here, although a last-minute increase in the size of the EC delegation allows each of the Community's 12 member-nations a delegate. Still, Mr. Matutes and other European officials count on the EC's stature as the Middle East's largest trading partner to put its regional role back on track. Europe's one bright spot at the conference is host-country Spain, which along with the US and the Soviet Union, will have diplomats assigned to each of the conference's delegations. Spanish officials insist Spain's role is simply to provide the difficult talks with a well-organized and cooperative meeting site. But the Spanish say their diplomats, with a long tradition of putting out feelers and acting as mediators between the Israeli and Arab communities, will be ready to assist if there is a role to play. "Our role is to provide the site for these talks, but our place is to remain neutral," says Jose Maria de Areilza, a prominent former Spanish diplomat and one-time foreign minister. "That's how we can best serve this process." Mr. Areilza knows whereof he speaks. As Spanish ambassador to Washington in the 1950s, he was contacted by prominent American Jewish leaders as a test of Spain's willingness to attempt to establish Arab-Israeli contact. This was the beginning of a recurring role leading up to the selection of Madrid as the conference site.