British Foreign Secretary Lord Carrington opened a major initiative today to solve the intractable Rhodesia dispute, saying there was "very real hope" for a settlement and calling on the rival sides to compromise.

The British-sponsored constitutional conference brought together the warring factions for only the second time in the 14-year-old dispute, but the mood of opening session emphasized the difficulties facing Carrington.

Rival delegations headed by Zimbabwe-Rhodesian Prime Minister Abel Muzorewa and rebel Patriotic Front leaders Robert Mugabe and Joshua Nkomo refused to talk to each other or even acknowledge each other's presence in historic Lancaster House, scene of numerous negotiations to end British colonial rule in Africa.

Both sides maintain they are here simply to talk to the British, as the power that can grant independence, and that the presence of the other side is irrelevant.

Tonight, the Patriotic Front boycotted a reception given by Carrington, saying it could not join in a social occasion with Muzorewa's black-led government, which it accused of "acts of banditry and aggression."

It would be the same thing as having the member of the Irish Republican Army who killed British hero Lord Mountbatten last month "come to a social dinner with Lord Carrington," a Patriotic Front spokesman said.

There has been concern that one of the sides might pull out of the conference, thus leaving the escalating seven-year-old war, which has killed more than 20,000 people, as the only way to solve the dispute.

Carrington issued a veiled warning to the parties, saying diplomatically: "I do not believe that the people of Rhodesia will readily forgive any party which deprives them of this opportunity to settle their future by peaceful means. This is a thought which should be in our minds throughout this conference."

Calling for "a willingness to compromise," Carrington said, "It is illusory to think that any settlement can fully satisfy the requirements of either side."

He painted a grim picture of what the alternative -- failure -- would be by comparing the current situation with 1976 when the various factions failed to reach agreement at a conference in Geneva.

"Since 1976, the number of men under arms on both sides has more than doubled. The war has spread into neighboring states. The toll in casualties inside Rhodesia and in the neighboring countries has continued to rise. Neither side has infinite resources. The price of failure . . . would be further prolonged bloodshed and further destruction of the life of whole communities," he said.

Carrington emphasized that drafting a new constitution for an independent nation was the first priority of the conference, saying, "We should first seek agreement on our destination -- which is the independence constitution."

Every since the conference was first proposed as a result of last month's British Commonwealth conference in Lusaka, Zambia, Britain has insisted on a step-by-step approach rather than putting all issues on the table as was done at Geneva.

British officials have said they will tackle the more difficult issues of disposition of the rival military forces and transitional arrangements leading to an election only after agreement is reached on a constitution.

This means, in effect, that there will be a two-phase conference if any success is achieved. The Muzorewa government, which contains strong elements of white-minority control preventing it from obtaining international recognition, will be called upon to give up elements of white authority contained in the constitution negotiated with former prime minister Ian Smith.

The Patriotic Front appears to have a problem with the British approach. Mugabe said in a BBC interview today that "political and military power go together" and the question was whether the British were prepared "to discuss the two side by side."

Mugabe reiterated the Front's stand of wanting to form the core of the military in any settlement, something that is unacceptable to the 230,000 white minority in the 7 million population.

Britain has sketched the outline of a draft constitution and Carrington said further suggestions are possible.

The opening of the conference was marked by heavy security measures as police lined the route the leaders took through Pall Mall, past St. James's Palace, home of the queen mother, to Lancaster House, an ornate 19th century mansion where Chopin once played for Queen Victoria.

About 100 Patriotic Front supporters lined one side of the route, singing African chants and holding posters with slogans such as "All Power to the PF."

Across Pall Mall about 50 predominantly white demonstrators shouted their backing of Muzorewa and Smith, holding posters telling their leaders to "stand firm." One black group chanted: "Hey, hey, Joshua Nkomo, how many kids did you kill today?"

In his speech, Carrington did not call the conference the last chance for a peaceful settlement, as many have done, and urged participants to look to the future rather than past failures "to lay the foundations for a free, indepenedent society."

here are still plenty of difficulties facing Carrington, who was the only speaker at today's opening session. Today he managed to thwart a Patriotic Front demand to change the order of seating so the two opposing sides would not be facing each other.