Supporters of the banned Solidarity union movement staged street demonstrations against martial law in a number of Polish cities today, but response to a call for an eight-hour nationwide strike was spotty.

The demonstrations, in which as many as 3,000 persons gathered here and in Wroclaw to mark the second anniversary of Solidarity's legal registration, were quickly broken up by elite ZOMO riot police using tear gas, water cannons and flares. They were considerably smaller in size than the last major round of coordinated street protests on Aug. 31.

At a press conference, the government spokesman, Jerzy Urban, said the day had ended in "complete defeat for the Solidarity underground and its foreign supporters."

Polish television reported that 800 people were arrested in demonstrations in seven cities, with 10 demonstrators and 17 police injured.

While it is difficult for foreign journalists to gauge the real extent of today's protests in view of the lack of full information from around the country, there seems little doubt that they fell well short of the hopes of Solidarity's underground leadership. The strikes had been intended as the first stage in an escalating series of protests, culminating in an all-out general strike next spring.

Interviews with workers outside factories suggested that, while a large majority still sympathize with Solidarity's aims and condemn its legal dissolution last month, they are generally unwilling to risk the severe penalties under martial law for participating in strikes. At the giant Lenin Shipyard in Gdansk, workers confessed that they were simply afraid to strike after being placed under military discipline following a two-day protest in October.

"Some of the younger workers wanted to strike, but the older ones refused to join them. We're being closely watched all the time by the military and the secret police. It's not the right moment," said a worker at a telecommunications factory .

Another explanation for the sporadic response to the strike calls was the exhaustion felt by many Poles after 11 months of martial law. Numerous strikes and demonstrations have so far failed to make any significant impact on the government beyond providing pretexts for further repression.

The Roman Catholic Church dissociated itself from today's protests, preferring to work instead toward a successful visit by Pope John Paul II to his homeland next year. The police were also particularly active in the past few days, arresting underground activists and warning known Solidarity supporters against taking part in strikes.

Spokesmen for the military regime have accused Western governments, and particularly the Reagan administration, of fomenting the unrest. Tonight it was announced on television that a U.S. citizen, identified as Roman Laba, had been arrested as "a spy" and accused of maintaining contacts with underground Solidarity activists.

The television announcer described Laba as a postgraduate sociology student with the Polish Academy of Sciences who had traveled to Poland many times. He said that many underground documents had been found in Laba's possession.

Official relations between Poland and the United States have deteriorated following the tightening of American trade sanctions.

[In Washington, President Reagan issued a statement accusing the Polish government of "declaring war on its own people."]

In Warsaw, some 3,000 people gathered near the supreme court building where Solidarity was formally registered exactly two years ago as the first independent trade union in the Soviet bloc. Shouting "End Martial Law" and "Free Lech Walesa," the name of Solidarity's interned leader, they started marching in the direction of the central Victory Square, but were stopped by a heavily reinforced cordon of ZOMO riot police.

The demonstrators were dispersed with tear gas, but later formed into smaller groups. There were minor clashes in Warsaw's Old Town district and near the university and Communist Party headquarters. Nearly 300 arrests were reported.

A floral cross laid in honor of the late primate of Poland, cardinal Stefan Wyszynski, was swept away by bursts of water cannon fired at the demonstrators. The cross had been decorated with portraits of Walesa, Solidarity signs and leaflets calling for protests Thursday.

Demonstrations were also held in the southwestern city of Wroclaw and in Nowa Huta, the scene of violent rioting last month.

A Western reporter in Nowa Huta said that some 1,500 workers managed to form a procession outside its steel works despite heavy police patrols. But a traditional route for protest marches was blocked by thousands of ZOMO and the demonstrators were forced into side streets.

In Wroclaw, up to 3,000 demonstrators were reported to have battled with police into the early evening. At his press conference, Urban denied Western news agency reports that as many as 15,000 Solidarity supporters had gathered initially.

Urban said that attempts to stage strikes had included what he described as "several desperate acts of sabotage." He cited a roof set on fire at a power plant, toxic gases thrown into workshops, slashed bus tires and attempts to cut off electricity in factories.

At the Warsaw steel mill this morning, workers were greeted with a loudspeaker announcement that the plant had lost 20 million zlotys ($250,000) due to sabotage in the cold rolling mill during the night.

According to Urban, some "work stoppages" did take place at medium-sized plants. A Western reporter in the southern city of Czestochowa quoted workers there as saying that at least one department of the large Bierut steel mill had gone on strike.