So the Soviets have troops in Cuba, and the politicians are alarmed, and the SALT pact's imperiled, and we're menaced because there they are, only 90 miles away .

The week after Labor Day in Washington, probably even more than in the rest of the country, marks the real beginning of the New Year. Congress returns, the political season begins, the newsrooms are filled once more, and everything points to a fresh start, the end of the '70s, the approach of a new decade with all those new issues we're supposed to be pondering -- economic austerity and energy shortages, simultaneously rising inflation and unemployment, declining national productivity and increasing ineffectualness of the political system.

For a writer resuming his Page Three perch full time after almost a year's absence and returning, as always, filled with wonder at the forward-looking working of Washington, it's comforting to find so many things still familiar.

For 10 or almost 20 years now, little has changed: our vigilant intelligence experts peer at secret photos of the Cuban countryside and once again find tents and other equipment in the open, with troops on maneuvers -- armed, no less -- and Russians to boot.

Clearly their presence poses a direct threat to the United States, alters the balance of power in the Caribbean and brings the Monroe Doctrine into play. The buildup of these two to three thousand troops has taken place gradually and clandestinely. Like the missiles of a generation ago, they arrived hidden in the holds of ships . Something must be done.

Why we didn't know immediately about this new danger raises the most profound implications: An intelligence gap of frightening proportions exists, and something must be done about that .

What becomes news and why remains an arcane subject. In the case of news about Cuba with major U.S. domestic political import, a Florida politician normally begins sounding the alarm. So it was with the missile crisis of 17 years ago, and so now with the -- what? -- crisis.

On Tuesday, July 15, Sen. Richard Stone (D-Fla.) publicly said he had information that the Soviet Union had placed what he called "combat-capable personnel" inside Cuba. He demanded that the Carter administration tell the nation what it knew about Russian troops there. If Stone's news made the papers, including The Post, I can't find it. That was the day of the Cabinet resignations, coming right after Carter's "malaise of the spirit" speech, and those events dominated the headlines.

The next Friday night ABC News broadcast a national TV report, in prime time, saying a brigade of Soviet troops, possibly numbering 6,000 men, had been moved into Cuba within recent weeks. Saturday morning in a three-inch Associated Press story printed at the bottom of page A6, the Post first reported that news under a headline reading: Network Says Soviets Sent Brigade to Cuba

One wekk later, in another Saturday page six story, The Post referred to Stone's charges, but you had to look hard to find the reference, which came in a story about Fidel Castro's views on the new regime in Nicaragua. The 21st paragraph read: "Meanwhile, Sen. Richard Stone (D-Fla.) characterized as a 'whitewash' an assertion by Secretary of State Cyrus R. Vance that 'there is no evidence of any substantial increase of the Soviet military presence of a Soviet military base.'"

There the story rested as Carter went off on his voyage down the Mississippi, as the newsrooms emptied, as the pace of Washington in the summer slowed. And then, lo and behold, just as the Labor Day weekend began bringing life and the politicians back to the Capital, and just as a widely publicized conference of nonaligned nations was convening in Cuba, the story bloomed on page one of The Post under a headline: 2,300-Man Soviet Unit Now in Cuba

The source for this story wasn't the relatively unknown Stone of Florida, but Frank Church, chairman of the Senate Foreign Relations Committee, that old liberal-leaning softie who went to Cuba and conferred with Castro two years ago, who investigated CIA assassination plots against Castro and denounced them, who for years has been an advocate of easing Cold War tensions. Frank Church, who is up for reelection, had been home to Idaho, where they don't brook commies.

"The United States cannot permit the island to become a Russian military base, 90 miles from our shores," Church said sternly.

For the last generation the Soviet Union has supplied Cuba with half of its imports and nearly all of its sophisticated weaponry to back up an armed force of about 600,000, including reserves.

All this time Cuba has been a Soviet camp, and all this time Soviet military personnel and hardware -- sometimes "offensive," mostly "defensive," submarines and MIG fighters -- have been implanted in and around there. During all this time the United States has had more armed forces (about 2,500) inside Cuba than the Russians have had. They're at Guantanamo, our price for "guaranteeing" Cuban independence back in 1898.

But that was not the news this week in Washington. It was back to the Cold War. As a relic who survived those days, I found the rhetoric familiar -- the threat, the intelligence failure, the Communist springboard for rebellion. But something was missing. Then I switched on the TV set to hear a presidential hopeful, Sen. Howard H. Baker Jr. of Tennessee, speaking about the new Soviet threat. If we don't do something, he said, we're in danger of becoming a paper tiger.

Made me feel right at home.