Patrick Buchanan and I, believe it or not, have enjoyed a rather affable personal relationship in recent years notwithstanding the fact that we are political and personal opposites. But there is a line at which affability must yield to indignant rejoinder. Pat crossed that line in his piece on the contras and the Democrats (op-ed, March 5).

"With the vote on contra aid the Democratic Party will reveal whether it stands with Ronald Reagan and the resistance -- or Daniel Ortega and the communists," he writes of the forthcoming House vote on whether Congress should give the contra rebels another $100 million as requested by President Reagan.

This, of course, is not the issue at all. There is no reason why the Democratic Party (or the U.S. government) has to stand with either Ortega and the communists or with Reagan and the contras.

As a matter of fact, the Reagan administration now officially recognizes the Ortega government and has a full- scale American embassy functioning in Managua.

With its unofficial arm, the administration is at the same time trying to finance a CIA-organized "covert" or secret (the world's worst guarded secret) effort based in Honduras to recruit disgruntled Nicaraguan rebels to sabotage the government we are officially dealing with in Managua.

Recent reports coming out of Nicaragua and Honduras from both critics and former supporters of the contra aid program charge that two out of three contras are no longer fighting in Nicaragua but have been idling away the time since last October in Honduras base camps.

It is the contention of Buchanan and his administration allies that the Sandinistas will prevail if the United States does not finance the contra war against them. It is my own conviction and probably that of most congressional Democrats and many Republicans, that the Sandinistas will prevail regardless of whether we finance the contras.

All indications are that this is not a popular guerrilla struggle strongly supported by the Nicaraguan people at the grass roots. The contras seem to be lacking not only a workable strategy but also a passion to fight, as well as the help of their fellow Nicaraguans. Without these ingredients the contra cause seems doomed to failure.

So the choice before the Democrats in Congress is whether it makes sense to continue using American tax funds to back a hopeless cause in a tiny, impoverished Central American state or we should join our best friends in Latin America, our historical allies in Europe and most of the rest of the free world in backing the Contadora nations, which seek a negotiated settlement of the Nicaraguan conflict.

These negotiations may leave the Sandinistas in power, but that is where they have been since overturning the hated Somoza dictatorship in 1979, and that is where they will doubtless be even if we continue to pour American money and arms into the fading contra cause.

If the Sandinistas do not measure up to the democratic standards of Corazon Aquino in the Philippines, neither unfortunately do the contras, some of whom are recruits from the old Somoza national guard -- an organization despised by the majority of Nicaraguans.

President Reagan has been concerned at various times with the Sandinista proximity to Brownsville and Harlingen, Texas, but when asked about Pat's claim, "If Central America goes the way of Nicaragua they will be in San Diego," the president said, "Pat speaks for himself."

One fact seems clear: It is ridiculous to suggest that the grizzled old worldly wise Irish Catholic Democrat, House Speaker Tip O'Neill, knows less about the communist challenge than the brash, much less experienced Pat Buchanan.

"It would be a disaster for America to drop from the high road of smart diplomacy -- (in the Philippines) -- to the depths of gunboat diplomacy," said the speaker of Reagan's proposed military shipments to the contras. To that I can only say, Amen.