Romance took a back seat to international politics today as Alexei Semenov, stepson of leading Soviet dissident Andrei Sakharov, was reunited with his wife, Liza Alexeyeva, who was allowed to leave Russia following a 17-day hunger strike by Sakharov and his wife.

Although the young couple had not seen each other in 3 1/2 years, they spoke to a band of reporters waiting outside the customs office at Logan International Airport this afternoon not of honeymoon plans, but of the plight of their parents, who remain exiled in the industrial city of Gorki, and of the military crackdown in Poland.

"The joy of everyone who sympathized with me is darkened by the tragic events in Poland," said Alexeyeva, 26, her smile suddenly turning into an expression as stoic as her husband's.

Alexeyeva, answering questions through interpreter Tatiana Yankelevich, her sister-in-law, said of the Soviet Union: "There are hundreds of prisoners of conscience serving their times in the prison camps, and Sakharov is still in his illegal exile and we still do not know what awaits him."

The couple plans to hold a more detailed press conference at the New York Academy of Sciences Tuesday.

Alexeyeva, looking already Americanized in brown corduroys, boots, a gray sweater and a white shawl draped around her shoulders, said she was grateful for the public support she has received from the western political and scientific communities.

She held a pair of red carnations, the only sign of a romantic encounter between her and her husband, who married her by proxy in June. The couple declined requests to embrace or kiss for the cameras and did not touch each other during the brief airport news conference.

Semenov, 25, who temporarily dropped his mathematics studies at Brandeis University to press for his wife's freedom, warned of retribution against the Sakharovs for what his wife termed "one of the few victories" of the Soviet dissident movement.

"The KGB will certainly try to avenge this," he said, expressing fear for the safety of his stepfather, a Nobel laureate physicist, and his mother, Yelena Bonner. The Sakharovs are reported to be in good condition since ending their hunger strike Dec. 8 after the Soviet secret police agreed to allow Alexeyeva to leave the Soviet Union. She was granted her exit visa Wednesday.

Semenov had said earlier that he had spoken to his mother Wednesday and she reported she and Sakharov were "generally okay." Semenov said they are living on a diet of cottage cheese, sour cream, boiled and mashed vegetables and mineral water. "Unless pressure continues, the fate of our parents is unknown," Semenov said.

Late in the afternoon, en route to her husband's home in Newton, Mass., Alexeyeva got her first taste of American justice when she and Semenov were stopped for speeding.

Police officer Jimmy Riley of Brookline, Mass., said he did not know who was in the car he pulled over for going 55 mph in a 30 mph zone. "I thought I recognized the name," Riley said. "I got back in the car and started to write a ticket. Then a photographer told me who they were . . . I gave him a warning instead. They won't be fined.

"They were kind of surprised," Riley said. "They didn't know what to expect. Afterwards I said to the lady, 'Welcome to the country.' And I said to the driver, 'Your luck is changing.' Everyone was laughing at the end."

While Alexeyeva, accompanied by interpreter Yankelevich and her husband, Efrim, was flying to Boston after a Paris stopover, Semenov stopped to address a rally supporting Polish Solidarity at Faneuil Hall, where American dissidents plotted revolution against the British more than two centuries ago.