The Vatican has been host to Russian Orthodox clergymen and offered them assistance in hopes of capitalizing on "glasnost" to improve the lot of Roman Catholics in the Soviet Union, a Vatican official says.

In the past month, three Russian Orthodox officials have visited the Vatican and met with Pope John Paul II. Two Roman Catholic church leaders from Poland also visited the Soviet Union recently, and the Vatican newspaper devoted two full pages to an effusive report by one of them on a changed attitude toward religion by the Soviet leadership."The greater freedom the Russian Church receives could help the Roman Catholic minority profit from `perestroika' and `glasnost,' " said the Vatican official, using Soviet President Mikhail S. Gorbachev's terms for reforming society and greater openness.

"Therefore, I have realistic hope - not a fantasy - that the situation of the Roman Catholic church will be substantially improved in the not distant future," said the official, who has first-hand knowledge of the recent contacts. He spoke on condition his name not be used.

In June, the Vatican sent a top delegation to the Soviet Union to help the Orthodox Church celebrate the 1,000th anniversary of the Christianity's arrival in Russia.

"If the Vatican gives its support (to the celebrations), it is worldwide support," the official said in an interview Monday.

Starting in mid-November, three Russian Orthodox prelates paid separate visits to the Vatican. Archbishop Pitirim of the Moscow Patriarchate saw the pope on Dec. 1, accompanied by an official of the Soviet news agency Tass.