Poland's Roman Catholic bishops reportedly have drafted a strongly worded letter to the nation demanding the lifting of martial law, the prompt release of all persons interned by the military government and an end to "ideological pressure" against members of the suspended independent trade union Solidarity.

Meanwhile, it was disclosed that the wife of Polish labor leader Lech Walesa has accused the military authorities of holding her husband illegally and complained that she has never received formal notification of his detention.

The bishops' letter, drawn up earlier this week in the first meeting of the Polish episcopate since martial law was declared Dec. 13, is said to warn of possible protests, revolts and civil strife unless dialogue is resumed between the government and society.

It also reportedly demands restoration of the right of workers to organize into "independent, self-governing trade unions."

The text of the pastoral letter, which is expected to be read in churches soon, has not yet been published. But sources close to the church said it was intended to express forcefully the church's opposition to the military crackdown while restating earlier appeals for calm.

About 90 percent of Poland's population is Catholic, and the church is considered one of the most powerful institutions in the Communist-ruled nation of 32 million. Its position of strength is recognized by the martial-law government of Gen. Wojciech Jaruzelski and it has emerged as a key intermediary between the government and Solidarity.

The bishops' letter comes as private negotiations between the church and the government continue for the release of Lech Walesa and other interned Solidarity leaders. Details are scant but church sources said it is possible that a bargain may eventually be struck under which Walesa and some of the union's more moderate leaders would be freed.

Danuta Walesa's allegations are in a letter she sent to the public prosecutor in Gdansk earlier this month demanding an investigation into the affair.

Walesa, 38, was taken from his home in Gdansk early on Dec. 13. He was flown to Warsaw, but government spokesmen repeatedly denied that he had been interned.

Originally foreign journalists here were told that Walesa was holding talks with the government and was being treated with "all respect due" the leader of Solidarity. This claim was dropped once it became clear that he was refusing to negotiate in the absence of his advisers and other members of Solidarity's inner circle.

At recent press conferences, officials have refused to provide any details of Walesa's status. They have said only that he is under detention in the Warsaw area and receives visits from members of his family, government officials and priests.

In her letter Walesa's wife called on the prosecutor to "act in accordance with your duty for supervising arrests and obedience to the law." It was not known whether she has received any reply to her complaint, which was filed about a week ago.

According to the letter, there are only three provisions under Polish law for depriving a citizen of freedom: detention, temporary arrest pending investigation and preventive internment.

Danuta Walesa said she understood that her husband was not detained as that would be contrary to the Polish constitution, which states that police are allowed to hold suspects for a maximum of 48 hours before placing charges. If he had been temporarily arrested, she said, according to the criminal code she should have been notified.

The letter said the only other possibility was that Walesa had been interned under the martial-law decrees--"but this has been decisively denied by the authorities."

The conclusion, she said, had to be that Walesa was being held in "informal internment"--a clear violation of both Polish law and the new decrees passed by the military regime.

Danuta Walesa, who spends most of her time in Gdansk looking after her six children and awaiting the birth of a seventh, is believed to have visited her husband since his detention.

Walesa's refusal to cooperate has become a source of considerable embarrassment to the martial law authorities. The government initially had hoped he would lend his authority to reconstructing a new Solidarity trade union purged of "extremists" and intellectual advisers.

Privately senior government officials have accused Walesa of displaying "a lack of realism." There are reports that he spends much of his time listening to the Polish-language broadcasts of Radio Free Europe.

His first place of detention was the luxurious villa of a discredited former Communist Party leader, Tadeusz Wrzaszczyk, at Chylice, south of Warsaw. He is said to have been transferred to one of a group of buildings in Warsaw's Rakowiecka Street that includes the general staff headquarters, a prison and a hospital.

His exact whereabouts are not publicly known.

The government minister Walesa reportedly has seen most often is Stanislaw Ciosek, who is responsible for trade union affairs. He reportedly has refused to talk to Deputy Premier Mieczyslaw Rakowski, with whom he negotiated union matters in the past.