SEN. NANCY KASSEBAUM (R-Kan.) has a sensible formula for El Salvador. She and two Democrats, Daniel Inouye of Hawaii and Christopher Dodd of Connecticut, would give the administration part of the extra aid it seeks and consider giving more if the administration could show that Salvadoran government leaders were making a good-faith effort to negotiate with their opponents on the left. Her idea would be to keep the Salvadoran army and economy going and at the same time to strengthen the hand of Salvadorans--such as, for example, Archbishop Arturo Rivera y Damas--who believe a political solution is the best way out.

The Kassebaum formula, if it became policy, would mark a major departure. For a Latin revolutionary movement to be acknowledged by the United States as a legitimate claimant to power unquestionably would represent a blow to the sitting government. The reality is, however, that the guerrillas have established themselves as a force to be taken into account. The administration is right-- and the Kassebaum group agrees--that they should not be offered at the table power they have not earned at the polls. But a seat at the table is something else.

Are the guerrillas prepared to accept the lesser share of power they might reasonably expect to gain through the political process, rather than the full power they may aspire to win by the gun? Would they or their civilian fronts go to the table not so much to bargain out a political process as to erode the Salvadoran and American will to stay the course? There is reason to be skeptical about the relative weight of the left's guerrilla and civilian factions and about its contrary tendencies to total victory and to political compromise. That is, the usual uncertainties attendant to the opening of a negotiation are plainly visible. The Salvadoran left no doubt sees uncertainties of its own.

Negotiations presume a middle ground of adequate size and firmness to support substantial factions from both sides. Is there one left in El Salvador? We are encouraged by the judgment of the newly elevated archbishop, who has boldly sought to capitalize on the momentum generated by Pope John Paul II's recent visit. The archbishop thinks the guerrillas have no important popular support. But he is prepared to make real the government's paper guarantees of amnesty and safety for them. His effort to promote "dialogue" may offer a bridge between the divergent and mutually exclusive kinds of talks now being offered by the government and the guerrillas.