The two parts of Korea have agreed to talk to each other but what they are talking about amounts almost to two separate conversations.

They are so far apart in their pronounced goals that it would take an enormous and virtually unimaginable concession by one side to produce a serious dialogue ad end an enmity that has lasted a quarter of a century.

Saturday, delegates from North and South Korea sat down in the truce village of Panmunjom for the first discussions about unification since talks were broken off in 1973. There were handshakes and smiles all around and they even agreed to meet again in three weeks.

But interviews with sources from both sides here and in Tokyo suggest that they are hardly communicating on the same wavelength.

The North wants to take a single, long step -- the convocation of a North-South convention, or "whole-nation congress," which would bring union leaders, social groups, and officials together in one mass rally for unification.

According to the North's representatives in Tokyo, the product would be a confederation of the two countries. Each would retain autonomous social systems -- the North's socialist, the South's capitalist. The two governments would remain intact, administering their separate domains, but the two would be represented jointly abroad, sharing a single seat at the United Nations.

The South, in this plan, would continue to enjoy investments from abroad. American and European companies would stay in business. The North would continue receiving aid and technological assistance from the socialist countries.

The entire Korean peninsula would become a "Confederate Republic of Koryo," employing the name used for a unified Korea during the Koryo dynasty from 935 A.D. to 1392.

South Korea's view is much less grand and the country's leaders speak sarcastically of "unification" as a distant goal hardly worth discussing at this stage. "We are realistic enough not to expect a miracle," says one government official. "We are not going to wake up one fine morning and find ourselves unified."

What the South wants to talk about is a lot of small steps, one of which might lead eventually to unification. It wants to talk about economic cooperation, the exchange of divided families, cultural events and athletic meetings.

The process of bringing those about, the South argues, might produce a genuine thaw, enough to unfreeze a relationship made rigid by 28 years of war, military incidents, and ferocious propaganda exchanges.

Given those widely different approaches, it seems somehow unlikely that the two sides would be sitting down together at all and the fact that a series of meetings now seems to be under way is mystifying, even to some South Korean officials.

It ostensibly began on Jan. 29, when South Korean President Park Chung Hee proclaimed that his authorities would be willing to meet authorities from the North at any time and on any level.

The North responded enthusiastically a few days later with a proposal to create a planning conference and even named a date. The exchanges increased, earlier dates were suggested, and the result was Saturday's meeting at Panmunjom.

The South now contends that the North had merely snapped up the latest in a series of more or less similar offers from Park. This one was a bit more explicit and comprehensive, admitted one official, but essentially it was a version of previously submitted offers. The question, they contend, is: why did North Korea snap it up this time?

The South has its own answer to this question, an answer colored by its own perception of North Korea as a stagnating, isolated country ruled by an aging cult leader, Kim Il Sung, and turning with increasing desperation to outside forces for help.

In this view, North Korea is seeking out Western economic aid and technological guidance to revive its economy, just as its current chief mentor, China, is turning to the West for help in modernization. Twice last year it sent out feelers, through the leaders of Yugoslavia and Romania, seeking closer contacts with the West, but got no response.

It must be clear to the North, asserted one official here, that it cannot get closer to the West unless it comes to terms, or appears to come to terms, with the South. The United States responded to both feelers last year with the advice that the North should get together with the South if it wants an amicable relationship with the United States.

Some observers here believe that a reverse pattern may account for the South's approaches to the North. South Korea is increasingly eager to trade with socialist countries and has made no secret of its ambition to cash in on a piece of the new China trade. Socialist countries reject most overtures of that sort out of loyalty to the North.

So friendly negotiations with the North, in this view, could help South Korea open trade ties with the socialist countries. South Korean officials who make policy here deny that that is a specific goal at the moment but agree that better trade relations with socialist countries could be a welcome fallout.

Representatives of both governments dispute the widespread notion that the current discussions resulted from foreign pressures. North Koreans in Tokyo insist that China did not push them into the Panmunjom talks and South Koreans, for once, agree. Both take at face value Chinese Vice Premier Teng Hsiaoping's statement that he will support the North but will not force it to do something it does not want to do.

The South, meanwhile, says the United States had nothing to do with Park Chung Hee's proposal.

"There was no pressure from the Americans," said one official, "but we do of course have a longstanding understanding that we both want to see some movement on this peninsula."

Despite the enormous gaps between them, neither North nor South seems inclined to break off the talks soon Neither would like to endure the bad public relations image that would result from a sudden walk away from the table.

One official who has just finished reading and rereading a transcript of the Panmunjom exchanges said he could not fathom any of the North's motives except one. "They just want to keep talking," he said.