In what appeared to be the start of a major government counteroffensive against planned demonstrations next week, Poland's interior minister went on television tonight to accuse underground Solidarity activists of preparing molotov cocktails and other weapons for use against the security forces.

The minister, Gen. Czeslaw Kiszczak, said the Polish Army and security forces have sufficient strength to enforce a ban on public gatherings. He said the organizers of proposed mass rallies to mark the second anniversary of independent trade unions in Poland were "counting on bloodshed and putting human life in jeopardy."

The rare television appearance by Kiszczak, a leading member of the military council that administers martial law, reflected the alarm with which the authorities view the protests and their determination to suppress any demonstrations. The stage thus seems set for a major trial of strength on the streets between the government and the Solidarity underground.

In its attempt to ensure law and order, the government clearly is seeking the backing of the powerful Roman Catholic Church. The primate of Poland, Archbishop Jozef Glemp, has spoken out several times against street disturbances, which he regards as counterproductive.

The church has been allowed to hold its own mass rallies to celebrate the 600th anniversary of the country's most sacred religious shrine, the Black Madonna, in the southern city of Czestochowa. The celebrations reach a climax Thursday when more than a quarter of a million people are expected to turn out for a sermon by Glemp outside the monastery of Jasna Gora.

A leaflet campaign announced by Solidarity as a prelude to mass street rallies has had very limited success. But, in view of the suspension of trade unions and other representative bodies of public opinion, neither side can be sure what will happen next Tuesday.

The government tactic has been to throw Solidarity off balance by cracking down in advance on the slightest sign of protest. A floral cross that had been a symbol of defiance in Warsaw's Victory Square has been dismantled permanently,the square itself was fenced off, and patrols of militamen have been stepped up.

At the same time, authorities have attempted to reassure workers that they regard the labor unrest of August 1980 as "justified" in view of the mistakes of the former Communist Party leader Edward Gierek. Tonight Kiszczak went out of his way to repeat assurances that the government would press ahead with political and economic reforms and the relaxation of martial law.

Many Poles, however, are skeptical that reforms can be pushed through in the absence of an independent body such as Solidarity as a driving force for change.

The interior minister promised that underground Solidarity activists who came out of hiding would be handled leniently but warned that stern action would be taken against anyone caught organizing or participating in demonstrations.

Kiszczak said the security forces were aware of plans to stage a rally in Warsaw next Tuesday by collecting people at four or five central points. Similar demonstrations are planned for other major cities.

"It's falsely claimed that these are going to be peaceful demonstrations. Why in that case do they prepare crowbars, clubs, molotov cocktails, sharpened sticks to puncture tires, and other dangerous weapons? They are also preparing medical points to assist the victims of these disturbances," Kiszczak said.

Insisting that public order would be maintained at all costs, Kiszczak added: "Nobody in this country or abroad should have any illusions that it will be possible to stage street demonstrations in Polish cities for the benefit of foreign television."

As in earlier periods of tension, the Polish authorities have put much of the blame for continuing resistance to martial law on the West and particularly the United States.

Western journalists based here have been accused of filing false and incendiary reports and, in the first action of its kind, the Pulitzer Prize-winning correspondent of The New York Times, John Darnton, had his press credentials suspended last week. The suspension was lifted today following retaliatory action by the U.S. State Department against the correspondent in the United States of the Polish Communist Party newspaper Trybuna Ludu.

The authorities also are seeking to make an example of people arrested during comparatively minor disturbances earlier this month.