The trauma of the murder of the Rev. Jerzy Popieluszko presents the Polish government with a formidable problem: how to retain the modest degree of public credibility it had begun to gain after this summer's political amnesty.
There is only one way to do that. It is to pursue the case of the slain Roman Catholic priest with the kind of vigor and openness displayed from the start - however damaging the exposure might be.
The concern that wrong-doing and flagrant abuses of the law by the police and political establishment might be uncovered grew Sunday when unnamed persons who attended Fr. Popieluszko's autopsy claimed he had been beaten, gagged, and tied up being thrown in the reservoir near Warsaw where his body was found Oct. 30.
Three policemen have been charged with abducting Fr. Popieluszko. An Interior Ministry spokesman said they are expected to be formally accused of murdering him. Two Interior Ministry colonels have been arrested in connection with the affair and a general has been suspended from his duties.
But unless justice is - in the words of one of Britain's great law lords - ''manifestly seen to be done,'' the government's credibility will fall even lower than it did following the imposition of martial law in December 1981.
Shortly before Popieluszko was abducted, a hopeful economic note had appeared as most of the Western Europeans decided to terminate their quarantine of Poland.
For Gen. Wojciech Jaruzelski's Poland, the Western decision presented hopeful prospects. It could mean a rescheduling of Poland's massive debts and access to fresh credit. Further, the West Europeans might induce the United States to lift its stringent sanctions and its veto on the crucial issue of Poland's admission to the International Monetary Fund (IMF).
Without such assistance, the current strains on the economy can only intensify. Some of the most realistic officials concerned say that would drag the country to the brink of a new crisis, potentially more dangerous than the explosion of 1980-81 itself.
It is possible that General Jaruzelski commended himself to his Western visitors as a moderate man committed to national conciliation - to such issues as self-government in economic enterprises, more place for non-communists in public affairs, and, above all, installing rigorous respect for law in place of manifest police (and Communist Party) abuses of legality.
Even so, the outlook is far from bright. For, however inclined Western governments might be to help, financial aid on anything like the prodigal scale of the 1970s simply is not available. Moreover, new credit will be subject to strict conditions.
But if the government falters in its pledge that henceforth the rule of law is to prevail, all this may not matter. Such a failure would make real improvement in the economy (in terms of labor discipline and productivity) or a genuine implementation of reform out of the question, sober-minded officials in Warsaw acknowledge.