The government of Paraguay yesterday vehemently rejected an international report accusing it of "constant violation" of human rights, including illegal imprisonment, possible murder and the use of "every form of cruelty" in dealing with prisoners.

The government described the report, issued by the Organization of American States Commission on Human Rights, as "tendentious, unfounded" and "sensationalist."

The strong rejection provoked the most heated exchange thus far between human rights advocates and the representatives of rightist military governments at this year's OAS General Assembly, which began here last week.

Alternately waving the document and a fist in the air, Paraguayan OAS delegate Luis Argana told the assembly that the report was based "not on concrete evidence, but on allegations" by "mercenaries" opposed to the government.

Shaking his own fist, rights commission chairman Andres Aguilar said OAS had shown a "Franciscan patience" with Paraguayan stalling tactics and a refusal to allow an on-site investigation in that country. He described the human rights situation in Paraguay as a "chronic evil."

For the past 30 years, Paraguay has been governed under a state of siege which has continually been reimposed by President Alfredo Stroessner, an army general who has been reelected to successive six year terms since 1954.

Since the commission issued its first report on Paraguay in 1962, the government has repeatedly refused to allow a full inspection team to investigate allegations of human rights abuses there. While Paraguay ostensibly agree to an inspection last year, it subsequently refused to set a date for the commission visit. This year's report is an updated version of denunciations compiled in previous years.

Sources within OAS said the commission felt it had been "deceived" by recent signs that Paraguay would co-operate, and that Aguilar was extremely surprised by the strong Paraguayan presentation yesterday.

Confrontations such as yesterday's were the rule rather than the exception at last year's OAS general assembly, the first since the new Carter administration made human rights a keynote of its foreign policy in Latin America.

Last year, Uruguay and Chile were the focus of accusations of rights violations by the governments of Venezuela and the United States, in addition to the commission. Both charged their accusers with using human rights as a tool of political interference, and presented impassioned denials and defenses of the actions of their military governments in the face of what they described as terrorist threats launched by international communist forces.

While Uruguay was the subject of another damaging human rights report this year, its defense was markedly toned down. OAS delegates from both Uruguay and Chile concentrated on the progress they said their governments have made in restoring civil liberties and promises for the future.

The delegation from Argentina, another of Latin America's military regimes accused of rights violations, has also largely kept quiet during this year's session, a situation which one government official attributed to "orders from the top."

While Argentina last week invited the OAS rights commission to conduct an inspection there, it is still unclear whether investigators will be able to visit Argentine prisons and speak with political detainees. The Argentine government has said OAS could talk with judicial and government officials, and the commission is currently negotiating to expand its inspection to include tours of alleged secret prisons where torture has been alleged.

But what OAS spokesmen had described as a new "maturity" and a "positive climate with relation to the human rights commission" in those countries where violations are alleged was at least partially belied with yesterday's Paraguayan presentation.

Describing "cruel invasion by guerrillas" from surrounding countries as a necessity for the continuing state of seige, Argana cited a number of alleged aggressions against Paraguay between 1958 and 1961.

Argana described one case of alleged torture and murder recounted in the report as "comic opera rather than tragedy." Rather than being killed at the hands of security police, as the report alleged, Argana said the subject in question had been a "poor victim of failed romance" who had been stabbed by a jealous husband in the bed of his mistress.

"I have proof of all these cases," Argana said, "not of just this one, but of all of them."

Gale McGee, the U.S. ambassador to OAS, called the report "sobering and disturbing" and said that if the government of Paraguay found it false, Paraguay should "be eager to have the commission visit" to resolve its differences with the organization.