Only minutes before it began, no one seemed sure there would actually be a demonstration. The maze of cobbled streets in the old city were filled with more people than usual, some of them apparently genuine shoppers, but most simply ambling, waiting, darting tense glances at each other.

Suddenly, at precisely 4 p.m., there were thousands of them, packed shoulder to shoulder in a mass of bodies stretching along the main thoroughfare from the old market square, past St. John's Cathedral to the royal castle where Old Town begins. It was as if they simply had materialized out of the gated doorways and painted plaster walls.

For a few moments again, no one seemed to know how to proceed. No leaders rushed to the cathedral steps, no speechmakers arose. Then, from those packed tightest in front of St. John's, there was a rustle, and a little shoving, and high above, where everyone could see it, a red and white Polish flag was raised, the word Solidarnosc (Solidarity) scrawled across it. The crowd drew in a collective breath and expelled it with the energy of months of pent-up emotions in a roar that swept the narrow avenue from end to end.

"Sol-i-dar-nosc, Sol-i-dar-nosc," "Release the detainees." "End martial law." "Free Lech," the latter a reference to Lech Walesa, the detained leader of the independent Solidarity trade union movement.

The chants began to overlap each other as, one by one, more flags were drawn from shopping bags and jackets and unfurled. They sang the Polish national anthem, and old women leaning out of windows overhead began to weep.

Later, the government said the demonstrations and street riots that swept Poland last Monday were composed mostly of young people and students--understandably frustrated by conditions in Poland today, but not representative of the population as a whole. That is not true, and is belied even by official arrest statistics showing that, of 271 persons arrested in Warsaw, less than half were classified as students, or of student age.

Although the Warsaw protests degenerated through the night into city-wide clashes between police and relatively small groups of youths, the people who came to Old Town were working men and women, families with children riding on their fathers' shoulders, older couples and men proudly wearing World War II resistance buttons, as well as students.

More to the point, in the view of senior advisers to the suspended Solidarity trade union, is the correct observation by Poland's Catholic Church hierarchy that the demonstration was called, not by what remains of the elected Solidarity leadership, operating from underground since martial law was declared last December, but by more radical--and more impatient--activists.

With Walesa and other union leaders held in detention by the martial-law authorities, the most senior official still at large is Zbigniew Bujak, president of the union's Warsaw chapter. He is exerting his leadership through clandestine bulletins and underground meetings.

Yet Bujak, according to Solidarity advisers in the church, did not call for the Monday demonstration, nor for the peaceful march under Solidarity banners that preceded it on May 1.

"He and the other officials at large don't control" these kinds of activities, an adviser who has been in contact with Bujak said. "They are the old, radical activists, but they are much more moderate now. They are looking for official status, thinking in political terms. Some of them have become real politicians.

"These new ones, committees in the factories, are pushing Bujak faster," he said. Among the possible forms of protest the leadership had been discussing were "maybe a small demonstration every month on the 13th," the monthly anniversary of the Dec. 13 martial-law declaration, "with 200 people in each city. Perhaps to have people wear Solidarity badges" or take an ostentatious walk around the block at the hour of the government's nightly TV news broadcast.

"These things are efforts to survive while the negotiations were beginning," he said, "but after five months it's not enough."

Although some government officials hint obliquely that high-level, substantive talks with Solidarity leaders have taken place, this source and others deny it. Now, following the demonstrations, the prospect that they will happen is seen as even more remote.

"The demonstrations could push Premier Wojciech Jaruzelski to become more hard-line," the adviser said. "Up to now, he hasn't even been able to negotiate openly. Now, how can he?" even in private.

Even if talks began with Walesa in private while he is still detained, the adviser said, there is little optimism over the outcome. "I was in Gdansk in August 1980" when Solidarity began, he said. "I saw the beginning of Walesa. He was created then; he had an instinct, the smell for it. But he doesn't act alone. He needs the people, the confrontation," to perform.

Still, he said of the government, the increasing impossibility of agreement "is their fault. They waited too long."

One now-disillusioned former government supporter, who once held an influential job, talked about his son, a Solidarity activist who spends his time running off clandestine bulletins and organizing. Their arguments over the proper way for the opposition to proceed burst into the open last weekend as the Monday march was being planned.

"I counseled restraint," he said. "My son told me that if everybody were like me, August 1980 would never have happened.

"I have to admit he's right."

As the protesters were chanting and singing outside St. John's Cathedral in Old Town, those on the outer fringe, at Castle Square, were just beginning a face-off with several dozen uniformed police. Backed by water cannons, tear-gas launchers, and a row of vehicles, the police waited several minutes as the crowd taunted them, alternately crying "Gestapo" and "Come and join us." As some protesters began tearing down red flags the government had erected for May Day, an officer warned through a bullhorn that such gatherings were illegal under martial-law regulations. The crowd whistled and jeered.

The first tear-gas canister sounded like a shot from a high-caliber machine gun, and once again the crowd held its breath. Many started to run down the narrow Old Town streets, pushing one another aside in panic. Others stayed and jeered as the tears streamed down their faces. Several picked up the canisters, which by now were falling in great numbers, and threw them back at the police.

On side streets, more police appeared. One bearded young man, recognized by a plainclothes policeman in the crowd, was dragged away by uniformed police swinging their clubs. Running after them, as the crowd parted, was an elderly woman, swinging her purse and yelling: "What are you doing? What are you doing?"

Yet even the police sometimes showed more respect than animosity. When a Polish photographer was caught in a crowd of rock-throwing demonstrators and taken to an officer, he was initially threatened with a beating and the destruction of his camera. The man in charge considered his protest, then asked to borrow one zloty from the photographer to call his superior and ask if photographs were allowed. He could not get through but, while keeping the film, politely handed back the camera, giving the photographer his telephone number and asking him to call the next day. He would, he said, check the regulations and see if he could give the film back.

Although some demonstrators stayed in the Old Town market square to fight, erecting barricades, gathering and throwing rocks--many of them getting their heads conked with the hard rubber clubs before being dragged off to waiting police vans--most simply ran when they rounded a corner and saw another police line. The uniformed men advanced, beating their shields with the clubs in a macabre rhythm, their faces covered with Darth Vader-like helmets.

The demonstrators worked their way out onto the main city streets in several directions, stopping just outside tear-gas range to turn and jeer again. They ran across main highways and yelled "Gestapo" back across the traffic. They were joined almost unanimously by passers-by who, between adding to the jeers, clucked their tongues at each other and remarked at the outrage of men in Polish uniforms chasing and beating Polish citizens.

Overall, it seemed more like the U.S. antiwar demonstrations of the late 1960s and early 1970s than the bullet-riddled street marches of pre-civil war El Salvador or of Chile. Nobody got shot, most escaped and, except for tear-gassed eyes, were relatively unscathed. On the side of the demonstrators, there was almost a kind of cheerful exuberance, together with heart-swelling patriotism. The police, while many were armed with real guns, obviously were not prepared to cross a well-drawn line to stop them.

Yet by midnight, when the last canister was heard being fired, and the stench of gas hung over the city, few were prepared to say that the next time would be quite so cheerful or that the line would not be crossed.