Advocates of contra aid in the White House and elsewhere fault the Central American peace agreement adopted in Guatemala last month for failing fully to protect U.S. security interests in the region. It would be truly remarkable if it did. This is, after all, an agreement worked out among five very poor and weak nations. One of them -- Costa Rica -- has no army; three others -- El Salvador, Guatemala and Honduras -- are politically unsettled; and one -- Nicaragua -- is fearful of and openly hostile to the United States. When they signed the Guatemala document, these countries expected the United States to make its own security arrangements, by negotiating directly with Nicaragua and also reaching whatever understandings it thought necessary with the Soviet Union and Cuba.

If the United States does undertake to satisfy its security concerns in this way, then the current peace initiative has a good chance of succeeding. If we do not, this significant opportunity for regional peace will be lost. The wars in Central America will become more bitter and destructive, and the security of every country in the region will be in greater danger. Hopes for democratic politics, economic progress and social justice will be disappointed.

The United States must resolve two key issues in head-to-head negotiations with Nicaragua and its Soviet bloc supporters. Secretary of State George Shultz, in recent congressional testimony, called attention to the most important of these: the United States cannot "permit a country as near to our borders as Nicaragua to become a place from which the Soviet Union and its allies can militarily threaten our friends or our country's national security."

The secretary is right. The United States must make sure that Nicaragua curtails its military ties to Soviet bloc nations and returns to normal state-to-state relations with them. Direct talks are needed to produce an unambiguous understanding with the Nicaraguan government on a process and timetable for ending weapons shipments from the Soviet Union and Cuba and withdrawing their military and intelligence personnel.

The United States should also be talking to the Sandinistas about arrangements for a cease-fire, as called for in the Guatemala accords. Because the Sandinistas are unwilling to negotiate a truce directly with the contras, it is crucial that the United States ensure that the terms and procedures of the cease-fire are acceptable.

The peace plan requires the United States to stop assisting the contras by Nov. 7 -- and the United States must comply if the peace is to become a reality. We must also insist, however, that a fair and verifiable amnestybe in place for contra soldiersand supporters. Those wishing to return peacefully to Nicaragua and become politically active must beallowed to do so -- free of intimida-tion or retribution. The best way the United States can support the contras is to ensure them the opportunity to join the political contest inside Nicaragua.

No matter that our support to the contras may have been ill-advised from the outset, or that the contra insurgency has hardened the rule of the Nicaraguan government, increased its hostility to the United States and driven it further and further into the Soviet camp. There is still no denying that the contras are now a potent bargaining chip for the United States. The contra war is bleeding Nicaragua, and the Sandinistas badly want us to stop financing it -- even to the point of compromising their revolutionary agenda. That's precisely why they signed the peace agreement.

The Sandinistas, meanwhile, also have a bargaining chip: the flow of Soviet weapons and the presence of military advisers. But they know that, however doubtful may be the current peace effort's prospect of success, they must take care to avoid blame for its failure. Contra aid from the United States is otherwise sure to flow at higher levels, and even the friendliest of their neighbors may look the other way.

Both chips have a very short half-life. Each is worth something only as long as the bargaining process is still in play. If the Sandinistas stonewall or if the United States drags its feet, the Nov. 7 deadline will pass, the game will end and the chips will become worthless. After that, contra aid will buy nothing but a guarantee of more Soviet support. More Soviet support, in turn, will buy nothing but continued contra aid. And the continuation of the two will buy nothing but more bloodshed and more destruction. The time to make a deal is now.

The United States faces a basic choice. It can join with its friends and allies in Central and Latin America in working toward peace within the framework of the Guatemala agreement. Or we can proceed alone and -- because of our overwhelming influence and power -- cause the peace initiative to fail. The writer, a former secretary of defense now practicing law in Washington, is chairman of the Inter-American Dialogue's task force on Central America.