If the speed with which freedom spread in Poland during the past 16 months stunned the world, the suddenness of its replacement by martial law has left Poles reeling with fear and despair.

The military government has managed to extend its control not only through simple muscle but also through a combination of psychological terror and a blackout of all but official information. So efficiently have these latter weapons been wielded that the feeling of national togetherness, which was the key to the success of the Solidarity trade union movement, has been all but shattered.

The goal appears to be to isolate people, to separate Pole from Pole, the people from the military forces, and Poland from the outside world.

Here in Gdansk, where Solidarity was born at the Lenin shipyards, the combined weight of the military and psychological tactics is seen, and felt, most clearly.

The success of the overall government strategy depends on its ability to put on a show of force that will frighten people sufficiently to persuade them of the futility of resistance. But this, the authorities seem aware, must be accomplished without large-scale bloodshed. Mass killings of unarmed civilians, such as took place in 1956 and 1970, could result in a backlash that would trigger immense soul-searching within the Army.

Poles have traditionally expressed pride in their Army. Having it turned against the nation has brought out a set of mixed emotions on both sides of the gun barrel.

One 19-year-old conscript, named Jan, insisted when asked that there were certain orders he and others would refuse to obey.

"There is no way I could force myself to shoot anyone -- even under the strict discipline of martial law, which amounts to wartime conditions," he said. "I'm not alone in that thinking. There will have to be special forces to do the dirty work."

The government does have such forces -- and they were particularly in evidence in Gdansk, as members of special military units, including the Red Beret paratroopers, were called in to take the shipyards this morning as I watched.

The storming of the Lenin shipyard was the climax of my trip to Gdansk, and to the center of Poland's new revolution, that had begun on Tuesday.

The Warsaw railway station was mobbed, with standing room only on the last train to Gdansk on Tuesday afternoon. All Poles have been told to return to the town or city in which their names are registered, and so the train was filled with businessmen whom the martial-law declaration caught out of town, people returning from vacations, soldiers reporting to their units, or students going home.

I was not stopped from getting on the train, and there were no identification checks during the 7 1/2-hour ride to Gdansk.

The mood of the travelers was one of uncertainty, of fear of what might explode and the possibility of repression on the job and at home. There was talk, but political discussion was rare and conducted only in whispers. The passengers seemed depressed rather than enraged -- or, if they were enraged, they did not show it.

University students standing in the aisles said that once school closures were announced Monday, they were told to pack quickly and go home, taking what they could carry and leaving the rest in parcels on their beds in dormitory rooms.

A woman from the agricultural school at the University of Siedlce said students there had been on strike for the past month, until they decided to call it off last Friday and start classes again this week in response to a call from the national union leadership and the Roman Catholic Church.

"Before, we had plans," she said. "Now there is nothing, nothing. Nobody knows anything. We haven't lost hopes. I can't say how the cause will be rewon, but I am confident somehow that things will turn better."

A Polish businessman, returning from a trip to Cuba, complained that on his Havana-to-Prague flight during the weekend, Czechoslovak flight attendants had blocked Poles from leaving the plane during a stopover in Frankfurt, apparently afraid some would want to seek asylum. Nobody even tried to get off, he said.

Changing planes in Prague, he said, Poles were forbidden to buy anything in the airport terminal, even though they had Czechoslovak money. The businessman, looking tanned from his Cuban stay, said he resented such treatment but "it's not new to us that we're treated that way."

A soldier said that he had ignored the military call-up for a day, preferring to extend his vacation, and he was now afraid he would be chewed out by his commander. He was worried, he said, about rumors that draftees like himself would not get credit for time served during the current crisis. Like many people, he seemed more concerned about the little things in his own life than the big political picture in Poland.

On the outskirts of Gdansk, a sign with eight-foot-tall letters was plastered on a wall along the tracks: "Countrymen. Save Freedom."

Although Gdansk is still papered with Solidarity posters calling for the release of detained leaders, strikes and protest demonstrations, attempts are generally being made throughout the country to eradicate all traces of the now banned movement, to which 10 million Poles once belonged.

In other cities, teams of workers are seen in the streets scrubbing Solidarity announcements off the walls. Under the martial-law regulations, even the possession by a private citizen of one of the millions of Solidarity leaflets that once swept the country has become a punishable offense. This week, television news gave prominence to a police raid on an apartment in Warsaw whose occupants had collected Solidarity literature, a clear encouragement to other Poles to destroy such material.

By military order, all popular entertainment in the country is banned. Movie houses, theaters, cabarets and discoteques are closed. Radio and television are limited to one state-run station each, which broadcast only official pronouncements and movies with a message like last night's film of the bloody 1956 uprising and Soviet suppression in Hungary.

Part of the propaganda campaign has been aimed at convincing Solidarity sympathizers that they can expect no help from the West. The statements of Western leaders that developments here are purely "Poland's internal affair" have been highlighted. Much was made of the fact that President Reagan did not see fit to interrupt his weekend at Camp David because of the Polish crisis.

The result is that many Poles complain of being thrown to the dogs once again, of being again betrayed by the West.

Soldiers are assigned to watch civilians, and other soldiers to watch their fellows. Although the militarized state-run television station found it necessary to retain some civilian employes, each is supervised by two privates who are in turn watched by a sergeant. No conversation is allowed; if this rule is broken, the soldiers are replaced by another pair.

Our train had arrived in Gdansk two hours behind schedule, just after the 10 p.m. curfew started. Across from the station, the Monopole Hotel, where Solidarity leaders holding a weekend meeting were rounded up Saturday night, appeared nearly empty, with few lights burning.

Most of the passengers decided not to chance being caught in the streets and settled down to sleep in the station. Outside, in the sub-zero cold, the city was eerily silent, with clusters of local militia and Polish Army soldiers milling about. I was stopped once on the walk to the nearby Hevelius Hotel by a group of militiamen who demanded to see my identification papers. One argued that I should be brought to the authorities immediately, but the others talked him out of it.

This morning, I was awakened at dawn by the sound of helicopters, six of them seen clearly from the hotel window, circling over the Lenin shipyards. Outside the shipyards themselves, a crowd of several thousand had gathered, held back by cordons of police.

Although striking workers inside had held the yards since the weekend, people said, the attitudes of police and soldiers had been relatively mild. During the cold nights of the strike, soldiers had handed over supplies of coal to keep the workers warm. As they held the crowds back this morning, there was some ribbing back and forth. One woman yelled, "Why don't you take off your helmets and come join us?"

The atmosphere changed when the special forces began their operation.

The gate had been smashed the day before, when several tanks charged the yard at noon. After they had pulled back, workers had put up a new, makeshift barricade. This time, however, the troops meant business. With the helicopters circling overhead, military vehicles and troops poured into the yards, met, according to the previously agreed Solidarity plan, by passive worker resistance.

As the last workers surrendered, handing over their identification cards and having their names recorded before being told to go home, a bulky, 6-foot-6 member of the elite internal security forces was overheard addressing a striker: "I don't know why we're letting you off so easily. You should all be hung, in my opinion."

Leaving this afternoon for Warsaw in a rented car -- the ordered closure of such agencies apparently had not reached Gdansk from the capital -- I passed again in front of the shipyards. The crowd of thousands had been pushed back from the gates to an intersection and the main street before the railway station was lined with civilians on one side and police in full riot gear on the other. The police began throwing tear-gas cannisters, some of which were caught by young people and thrown back.

On the outskirts of the city, the oil refinery was surrounded by tanks of the First Armored Division, their guns, although capped, pointing inside the facility. Driving on, I was stopped at an Army checkpoint, and my name was written down in a book.

There was significant truck traffic, but few passenger vehicles, along the 250-mile stretch to Warsaw, and the cold fog was so thick that it seemed unsafe to drive at more than 30 mph. A number of Polish Army trucks and one tank were seen broken down along the road. At a checkpoint manned by local militia, I was asked the name of my employer and told, before being allowed to pass, that I was not supposed to be traveling.