Leaders of the independent trade union Solidarity prepared today for a referendum on replacing the manager of Poland's largest industrial plant, a development seen as a key test in the growing campaign for worker self-management.

Union leaders appeared determined to hold the referendum at the Huta Katowice steel mill in Poland's industrial heartland despite government warnings that it does not intend to give up control over industrial enterprises.

Solidarity's local chapter claims 17,000 of the 19,000 workers at Huta Katowice as members.

The decision to go ahead with the referendum is expected to raise tensions in the current political struggle between Solidarity and the ruling Communist Party. The referendum, to be held before the end of the month, apparently was timed to coincide with the scheduled meeting of the Communist Party's policy-making Central Committee, which is expected to discuss the issue of self-management.

The union has already challenged the government over the issue of access to the mass media with a two-day newspaper strike last week.

It is unclear whether the increasing confrontation on these two crucial issues reflects posturing by both sides before the first congress of Solidarity next week or whether the gap between them on how to approach reforms of Poland's shattered economy is getting wider.

Polish observers and Western military attaches have reported an increased number of security forces in the Warsaw area. Riot police in full gear and trucks carrying equipment were seen yesterday in several parts of the city.

Tensions continue in the Radom area and in Olsztyn, where a newspaper strike entered its sixth day. In a related development, Solidarity leader Lech Walesa called on Polish journalists to tell the truth about Solidarity and its congress and to resist official pressures to conform to the party line.

"If this leads to reprisals," Walesa said in a statement to the journalists, "we shall protect you. Your honesty will will save Poland from new strikes. Truth is as necessary for Poland as is coal."

In another indication of tension, the deputy interior minister, Gen. Wladyslaw Pozaga, said today that foreign embassies in Warsaw and particuarly the U.S. Embassy have "intensified their espionage activities."

The general told the party daily Trybuna Ludu that "certain diplomats" were trying to recruit Polish citizens for espionage work and that in the past month "increasing penetration of foreign espionage agencies" has been recorded. He gave no examples.

So far, there are no indications that the government will accept a Solidarity offer to resume talks on union access to the media. Another nationwide strike against all daily newspapers has been threatened for next week.

The question of workers' self-management goes to the core of contemplated economic reforms. Solidarity sees it as essential. The government stand was made clear by Premier Wojciech Jaruzelski who said last week, "Unless the state remains in control over enterprises it would not be able to carry out its functions and act in the national interest."

Last night, the official Polish news agency PAP quoted the director of Huta Katowice, Stanislaw Bednarczyk, as calling for effort to "rebuild strong state authority in enterprises."

Solidarity, he continued, was trying to take over control of enterprises and if that happened, "the entire authority up to the ministerial level will become like a house of cards."

Bednarczyk, whose job is at stake in the scheduled referendum, said "many steelworkers have stopped believing that the authorities can do anything in this country." He added that a "strong state authority is the necessary condition for overcoming the current economic difficulties."

The ballot at Huta Katowice will have six questions, including the main one of self-management. It will ask whether management should "carry out the will of the majority" or continue to be responsible to state authorities.

Other questions include one on whether Bednarczyk should be retained as director and a general vote of confidence in either Solidarity's local committee or Bednarczyk.

The Huta Katowice situation arose from disputes over the twin issues of press freedom and workers' self-management. Solidarity lost confidence in the director after he voiced support for the government when it seized the local union's printing press on charges of anti-Sovietism.

The workers later placed a white-painted wheelbarrow in front of the director's office -- a symbol in Poland that he will be thrown out.

While the wheelbarrow was removed, the issue has become the focus of the union struggle for local autonomy. The government fears that the introduction of workers' self-management would bring about both economic and political decentralization, thus curtailing the power of both the party and the government.

Tonight, Solidarity lodged a protest with the government against the proposed increases in the price of bread and cereals, saying they violated earlier agreements.

The sharp increase in the price of bread was to have become effective today but was put off until Sept. 1. It may again be delayed because of union opposition.