It's an eerie day.
Under gray skies that match the drab gray-green fatigues of the helmeted, automatic pistol-toting antiriot squads, all Warsaw seemed poised for confrontation.
As I write, the sidewalks in the city center are bulging as usual with people , leaving work or the shops, and mostly, it seems, hurrying to get home.
At 4 p.m., an official Polish newscast says: ''Peace is unbroken all over Poland on this second anniversary of the August 1980 agreements.''
Work ''proceeded normally'' during the morning shift. The second shift started on time. ''No incidents anywhere in the country,'' the radio says.
After a low profile during the morning, the rapid afternoon buildup of security here has reached massive proportions.
The concentrations - truckloads of police and troops, water cannon, tear-gas weapons, and flocks of jeeps and command cars - are thickest at the four centers singled out by the Solidarity underground as the venue for its supporters and sympathizers to protest continuance of martial law and their loyalty to the union.
The foreign press center where this dispatch is being written is in the national theater. Back and front is a park of police and military vehicles.
They have just moved off, some in the direction of the square just outside the Old Town, one of the places chosen by the underground for a rally. Officers can be heard calling through bullhorns for people to disperse. There is a formidable force to beat off any endeavor to approach either the Palace of Culture - a Stalin gift to Poland after the war - or the city library. Both have seen action in previous martial-law clashes between civilians and police.
Despite the show of force, the authorities appear to be making an effort to keep things within bounds of restraint.
Away from the sensitive areas, police and military patrols, or the ''zomo'' antiriot units, are ambling slowly along the sidewalks in groups of six. An occasional car is stopped and its trunk inspected.
Although nothing serious has happened so far, the atmosphere remains tense. Many Poles are inclined either from conviction or by despair to stay away or get away from any possible ''danger'' zones.
''Only a lunatic would want to demonstrate against that,'' a Pole says, watching the force outside the Palace of Culture.
At 5 p.m. word comes from the long Marszalkowska shopping street of what sounds like the toughest incident yet.
(Crowds swelling on the sidewalks began to look like a demonstration and the security forces scattered them into a narrow off-street where they came ''under fire'' from water cannon and tear gas. It seems to have continued for some time but no would-be demonstrators managed to break the ring around the Palace of Culture.)
I watch as Zambow Square (leading to the Old Town) is cleared. Trouble erupts near a crowded tram stop on the street level below.
There are two Solidarity flags, but as the police move in the crowd disperses and most people jump on trams to get away.
Outside St. Anne's Church the crowd is sprayed by a water cannon. A riot squad lines up across the street and an officer shouts a warning that people have 15 minutes to leave the area.
Some youths down a little incline from the main street jeers. ''You should go away and study your history,'' the officer shouts.
Five minutes . . . three minutes . . . finally the line of troops advances. The first tear-gas shells and rockets are fired, then it becomes a fusillade.
The street is slowly cleared, the bystanders move on - but from the windows above, Poles look down on a scene many feel they have seen too often since Dec. 13, the day martial-law was imposed.
The troops are mainly young. Many, it appears, do not relish their job. They are quick to relax when the action is over.
Dusk falls over the city and there are still five or six hours to go in which tensions and tempers can rise to more serious dimensions than they have so far, either in Warsaw or the big provincial cities. Krakow at the latest word is, it seems, quieter with less of a police presence as always.
In Gdansk, the monument outside the shipyard gate - commemorating the workers who died in the 1970 riots - is ringed by police. There are reports that 5,000 workers gathered here, chanting Solidarity slogans and calling for Lech Walesa's release.
A police officer in charge says: ''The shipyard workers can come, they can pray or sing and lay flowers and stay as long as they please . . . but no one from outside.''
Warsaw Radio has just announced the seizure of Zbigniew Romaszewski, former member of the dissident KOR group and a leading Warsaw Solidarity activist.