In the old joke a Catholic priest is driving along when he smashes into the car in front of him. A stereotypical Irish cop comes along, looks at the damage and says, "Father, how fast was he going when he backed into you?" Remember that joke. It tells you something about the Reagan administration and Nicaragua.

From the White House now comes a bellicose condemnation of Nicaragua for what amounts to "backing into" both Honduras and Costa Rica. Larry Speakes, his master's voice, went into his moral-outrage mode after Sandinista troops had reportedly crossed into both countries: "The United States strongly condemns these actions and calls upon the government of Nicaragua to halt immediately any further action against its neighbors."

At no time, though, did Speakes mention that for some years now Honduras has been used as a staging area for the so-called contras -- anti-Sandinista guerrillas. Repeatedly, the contras have entered Nicaragua, killed both troops and civilians, blown up installations and created as much mayhem as possible -- and then have retreated to their haven in Honduras. It was only a matter of time until the Nicaraguans would go into Honduras itself.

As for Costa Rica, it, too, has sheltered anti-Sandinista rebels. The country has been the prime base for guerrillas under the control of Eden Pastora, the former Commander Zero, whose ties to the CIA are more tenuous than those of the contras based in Honduras. What is not clear is whether the government of Costa Rica, a democracy with no army to speak of, can in any way control guerrillas operating within its borders.

In legal terms, what is going on now is called "entrapment." The administration supports contras who use both Costa Rica and Honduras to stage raids in Nicaragua, and then cries foul when the Sandinistas give chase. This, though, is precisely what the Israelis finally did in Lebanon and what the United States did when Mexicans such as Pancho Villa had the effrontery to raid Texas border settlements.

Nicaragua's Sandinista leadership seems convinced there is nothing it can do, short of suicide, to please the Reagan administration and, therefore, it ought to just do what it wants to protect its own country. It seems equally convinced that the United States will invade Nicaragua someday. A Reagan adminstration military buildup in Central America -- seven airfields in Honduras alone -- has left the United States as ready as it ever will be to launch an invasion.

The Sandinistas' reading of the situation may or may not be accurate. In Washington no one seems sure. House Speaker Thomas P. (Tip) O'Neill is on record as saying that Ronald Reagan is determined to invade -- and that's all there is to it. Others say that Reagan is playing a huge bluff, that he's making the Sandinistas nervous, increasing pressure on them, causing internal discontent and -- atypically for an American president -- taking the long view and playing things out slowly. In time, with a little help from its enemies, the Sandinista regime will collapse.

Maybe. But history teaches that events have a way of getting out of control. If so, the Washington debate about the president's intentions may be moot. Already, the United States has simultaneously reaffirmed its Rio Pact commitment to Honduras and ensured that it would be attacked. The same is more or less true with Costa Rica. It has so rattled the cage of the Sandinista leadership that it may conclude, macho- like, that if it's going to go eventually, it might as well go on its own terms. To exhume a word from a previous era, things have a tendency to "escalate."

In condemning Nicaragua for doing what any nation with any measure of pride would have done long ago, the United States has gone the cop in the old joke one better. We're both driving the car and establishing blame -- and thinking we're so cute. But we've overlooked something. Soon it may not matter who's at fault. It will only matter that a collision has finally occurred.