British officials, apparently seeking to add a new element of pressure on the government in Buenos Aires to declare a formal end to the Falklands war, warned today that Argentine military prisoners on the Falkland Islands face possible death from exposure.

Two days after British ground forces completed their dramatic recapture of the islands, the commander of Britain's naval task force said hundreds of the prisoners were in poor physical condition and could die unless Buenos Aires cooperated in securing their release and safe return.

"They are already suffering from malnutrition, exposure, in some cases hypothermia, trench foot, scabies and diarrhea," said Adm. John Woodward in a statement. "There is no way I can shelter these numbers. Even feeding them for a week in present circumstances presents huge problems . . . . Meanwhile conditions are getting worse as winter arrives."

Military officials here denied they were using the issue of the prisoners as leverage to obtain a declaration from Argentina's ruling military junta confirming the complete cessation of hostilities in the South Atlantic. But Foreign Secretary Francis Pym told a radio interviewer that the prisoners were a "huge incentive" for the junta to cooperate.

Woodward used the figure of 15,000 prisoners but that number is now in question and the British said they were making their own count.

So far, the British have received no reply to their request for a formal cessation of hostilities with the mainland, transmitted yesterday through the Swiss Embassy in Buenos Aires. The sole Argentine statement was last night's televised speech by President Leopoldo Galtieri in which the general conceded that the battle for the Falklands capital of Stanley was over but warned "there would never be security or peace" in the islands if Britain attempted to reestablish colonial rule. He did not mention the prisoners.

British officials appeared both surprised and dismayed by Argentina's lack of response. Sources in the Foreign Office here, which is handling the diplomatic effort, had predicted yesterday the declaration would be obtained by tonight.

An aide to Prime Minister Margaret Thatcher said today Britain has sought help from other Latin American nations, including Brazil and Uruguay, in pressuring Argentina for a statement. In the meantime, he said, Britain would maintain its blockade zone 12 miles off the Argentine mainland, and would seek to continue Common Market trade sanctions on Argentina.

Without an Argentine assurance of peace, officials have said they would be forced to maintain a large and costly garrison of soldiers, aircraft and warships to defend the islands. There were also fears expressed here that pressure would mount on Britain from its allies to bring a halt to the conflict by agreeing to negotiate the issue of sovereignty over the Falklands with Argentina--something Thatcher has pledged she will not do.

So far, the Thatcher aide said, there has been no new pressure on London from the United States, which reportedly has viewed with alarm Thatcher's refusal to negotiate with Argentina. "I reckon Secretary of State Al Haig and President Reagan are very clear on our position and where our mind is and they don't waste their breath on it," the aide said.

In surrendering the remaining Argentine forces on the islands Monday night, Gen. Mario Menendez told his British counterpart, Maj. Gen. Jeremy Moore, that there would be no attacks from the mainland on British soldiers or warships off the Falklands. But Woodward and other military officials said that until a firm assurance was received from the junta, they feared new attacks by Argentine warplanes or submarines were possible. They said that possibility was diverting their attention from dealing with the prisoners.

"I have my usual defensive problem and now a major relief disaster on top," said Woodward. "If a choice has to be made, however, defense comes first. Thus the Argentines must appreciate that I cannot keep their troops dry and warm and fed while we are still subject to attack. They must face the facts and agree to cease all, repeat all, hostilities."

The 15,000 cited by Woodward was said to be based on numbers supplied by Menendez, was contradicted by Moore, who said other Argentine officers had put the figure at between 8,000 and 9,000.

Moore also dismissed concern about Argentine deaths from exposure, saying, "They have survived on the islands for some weeks."

Officials here denounced Argentine silence concerning the prisoners. "We are getting absolutely no cooperation whatsoever from the government of Argentina," said Royal Navy Commander John Fieldhouse told the press. "The condition of these prisoners is being worsened by the sheer disregard for their welfare by their own government."

As described by British military officials here, the major problem is not food and medicine, of which there are enough for the immediate future, but a critical shortage of shelter, warm clothing and blankets. Falkland temperatures have begun dropping well below zero at night, with Antarctic winds whipping through islands that are virtually barren of trees and other protection.

Officials said British forces, who have been on the ground for more than three weeks since landing at San Carlos, also were suffering from exposure. About 4,500 tents designated for British troops and for expected POWs were lost when the cargo ship Atlantic Conveyor was sunk by Argentine warplanes three weeks ago.

British Hercules cargo planes were reported tonight to be dropping blankets and clothing at Stanley. Fieldhouse also issued a plea tonight to the United States to assist in airlifting supplies.