NO ONE HAS YET come up with a good idea for a summit site. I would like to put one on the table: Managua.

Yes, I know its shortcomings, I was recently there for a few days. I know it's no watering place. In fact, it has no water at all twice a week. But to me, that's part of its charm for a superpower get- together.

It would do both Ronald Reagan and Mikhail Gorbachev good to call the switchboard at the Intercontinental Hotel and report empty faucets in the bathrom. The operator says brightly, "Oh, yes, that's right, no water in Managua every Tuesday and every Friday," as if she were speaking of a unique tourist attraction. It does wonders for perspective.

It's true there isn't much to see, unless you have an appetite for vistas of vacant lots, the legacy of the 1972 earthquake damage which has remained almost undisturbed. But as a cure for severe foreign policy afflictions -- in Reagan's case obsession and in Gorbachev's opportunism -- Managua is matchless.

If they spend the usual four days there -- and their stay should go from Tuesday through Friday -- they might come away with their minds blown and blow-dried about their illusions in Central America.

I'm not saying they would draw closer together. In fact, on the showerless days, they might want to have their one-on-one sessions from separate rooms, and they might well never get around to the subject of nuclear disarmament. It's a little hard to think about Star Wars when roosters are crowing on Main Street, and they may be too busy negotiating deals on soap, which is also in short supply, to concentrate on warheads.

But I think I can promise you that they will depart from the Sandino Airport ready to sign a bilateral, mutually verifiable freeze on superpower meddling in this basket case of a country, where it would be loco for either to persevere.

From Washington, Reagan looks at Nicaragua and sees another Cuba for Gorbachev, which is both a good thing and a bad thing from his point of view. Another Cuba means "communist expansion," more Castros, quarantines, sanctions. On the other hand, another Cuba means for Gorbachev another drain on the treasury for dubious ideological gain. It costs him a million dollars a day to keep Havana afloat. Nicaragua, he could see at a glance, would come at a figure about the size of Reagan's deficit.

From Moscow, on the other hand, Gorbachev looks at Nicaragua and sees another Vietnam for Reagan. Vietnam means an unpopular war, search and destroy, Rolling Thunder, pacification, Nicaraguaization, world opprobrium, havoc at home and God knows what.

Reagan could look out of his hotel room and see a place that looks as if it had already been bombed back to the Stone Age -- and think again.

He would undoubtedly be given a little taste of what would befall him if he decided to go all the way with the contras to liberate the country from the Iron Curtain.

Hundreds of Americans come to Nicaragua every week.

They are stricken by guilt over Reagan's hard hand here and caught up in the romance of the revolution. They come bringing medicine and moral support; they help with the coffee harvest. They ask for briefings at the American Embassy, and then chew out the briefing officer for the criminal insanity of Reagan's policy. They would be happy to demonstrate in the vacant lot under Reagan's hotel window -- and make his day.

Gorbachev would find no comfort in any strictly chaperoned mingle with the masses. Nicaraguans are incurably chatty people, and Gorbachev would find that the Sovietization has not gone on at the pace of Reagan's rhetoric. People talk their heads off about the government. They grumble incessantly about the shortages and the Marxist-Leninist mismanagement -- the general opinion in the streets is that the crowd in charge couldn't run Boystown, and desperately need mass crash courses at the Harvard Business School.

Conversation with the national directorate would not be terribly reasuring. Interior Minister Tomas Borge is a tough old Bolshevik, but otherwise, they are maddeningly "un-Moskovite," much given to lecturing visitors about values, the past and "evolving revolutions." Their anti-Americanism is complicated by their passion for baseball, jogging and not being invaded.

If Reagan and Gorbachev should take a little run into the countryside, they would bounce around on the potholed roads, and find an utter absence of any photo opportunities. The "right" shack would be harder to find than the "right" concentration camp.

I think that it is entirely possible that on the way back to Managua, they would fall to arguing about who had the right to get out first. Nicaragua is the kind of a place that would give "unilateral withdrawal" a good name.