THE SOVIETS AND THE SUMMIT : Baltic Secession a Touchy Issue for Mulroney : Canada: The prime minister must tread lightly, since he’s faced with his own threat of a breakaway by Quebec.

When embattled Soviet President Mikhail S. Gorbachev landed here Tuesday, protesters in the Canadian capital took advantage of his two-day visit to call for a tough stance opposing the Soviet economic blockade of the breakaway republic of Lithuania.

But Canadian Prime Minister Brian Mulroney seems unlikely to give them much satisfaction, for recent weeks have brought him face to face with a growing secessionist threat of his own, in the province of Quebec.

The Mulroney government has kept its language on the Baltic republics subdued in the days leading up to Gorbachev’s arrival, not only to show support for Gorbachev’s reforms but also to avoid sending the wrong signal to Canada’s restive French-speaking province.

“He’s probably aware that if you encourage this issue there, you can have the same thing here,” said Gerald LeBlanc, a Quebec nationalist newspaper columnist in Montreal.

No Canadian has forgotten what happened when a head of state visited Canada during an earlier bout of Quebec separatist sentiment: In 1967, French President Charles de Gaulle unexpectedly took to a balcony in Montreal and called out “Long Live Free Quebec!” to the crowd, igniting French-Canadian passions and shocking English Canadians.

Turbulence in the Soviet Union makes Mulroney’s domestic problems look small. Still, the two leaders are meeting at a time when Mulroney’s approval rating in the polls is the lowest of any prime minister in Canada’s postwar history.

In addition, the Gorbachev visit began just as Mulroney was trying to orchestrate a week of whirlwind “diplomacy” among Canada’s 10 provinces, sending an emissary across the country and holding an unusual series of one-on-one meetings of his own in the capital with the all-powerful provincial premiers.

The negotiations are a last-ditch attempt to save a package of constitutional amendments intended--when written three years ago--to appease dissatisfied French Canadians in Quebec. Three English-speaking provinces have been fighting the package, known as the Meech Lake Accord, and the divisions have grown so deep that numerous Ontario municipalities have voted themselves “English-only” towns. And Quebeckers are concluding that English Canada will never understand them.

Analysts are predicting that if the accord isn’t ratified by the June 23 deadline, the failure will prompt Quebec to set in motion a process of separation from English Canada.

In light of this prospect, the plight of the Baltic republics has captured the close attention of political observers in Quebec.

“I remember the day I heard that Lithuania had declared independence--I was glad,” said Stephanie Martin, a 23-year-old graduate student in Quebec literature whose deep but non-militant nationalism represents the thinking of many young Quebeckers. “I was thinking about (the Lithuanians), but I was also thinking about Quebec.”

But, while English and French Canadians have bickered, Canadians of Ukrainian and Baltic heritage have expressed deep resentment at any parallels drawn between Quebec and the restive Soviet republics.

“If Quebec had been treated since the 1700s the way Ukraine has been treated, there would be no Quebec,” said Lubomyr Luciuk, a Canadian professor of geography whose ancestry is Ukrainian. He pointed out that Quebec entered the Canadian confederation of its own free will, while the Baltic states were forcibly annexed by the Soviet Union in 1940.

And Quebeckers are allowed to choose their representatives from an assortment of political parties and enjoy as-equals negotiations with English Canada, rather than economic strangulation.

“I have no intention of spending my life in an outpost in Quebec suppressing my friends, who happen to be Quebecois , who want independence,” Luciuk said.

He was speaking at a “Baltic Freedom Days” luncheon staged by Canadians of Ukrainian, Baltic and East European descent to coincide with Gorbachev’s arrival. Canadians from these ethnic groups number more than 1 million, and they make up a sizable force in a country with a population of about 25 million.

Citing Canada’s reputation for following a foreign policy based on morality and acting as peacekeeper in world trouble-spots, they have been calling on Mulroney’s government to extend diplomatic recognition to Lithuania.

The protesters also are staging a round-the-clock vigil at the Soviet Embassy during Gorbachev’s visit. They will hold a rally in front of the Canadian Parliament today, where the Soviet leader is scheduled to have a private session with Mulroney.

There has been speculation that Gorbachev canceled a previously planned speech before Parliament because of the protesters, but some say he simply wished to save his message for Washington.

Amid pressure to grant diplomatic recognition to Lithuania, Canadian External Affairs Minister Joe Clark has promised only to seek “international guarantees” by which Lithuania could achieve a negotiated independence, one that wouldn’t endanger Gorbachev’s imperiled reforms.

Clark has said that Canada would be willing to help the breakaway republic establish government ministries and train bureaucrats, and he said the government is considering ways of shipping livestock feed into Lithuania via Poland to combat Moscow’s economic blockade. But he rejected suggestions that Canada break the embargo on oil and gas by sending in Canadian fuel.

“How sad it is that Western governments are intent on shoring up the last remaining empire,” said Father Sigitas Tamevicius, a Lithuanian priest who appeared at the protest luncheon with the red, yellow and green of his national flag pinned to his clothes. “How painful it is that excessive caution by the Western nations turned the threat of the blockade of Lithuania into reality.”