WARSAW -- Thousands of art lovers, churchgoers, academics and journalists have been lining up in the gray early-winter cold here to visit a modest Catholic church annex that almost overnight has become Poland's richest museum.

The archdiocese museum, opened in 1980 as part of a broad effort by the church to nurture independent culture in Poland, has been known until now mainly for its exhibitions of painters and sculptors who shun the communist-controlled art establishment.

Recently, however, the museum took on an entirely new role. Following nearly a year of preparations, it has begun to exhibit a huge new collection of European painting, including works by masters from Rembrandt to van Gogh, donated to the church by an e'migre' Polish couple.

The stunning gift, which has made the Polish church as important a curator of European art as the Polish state, is the crowning work of two extraordinary benefactors: Zbigniew Porczynski, an Auschwitz survivor who became a hugely successful chemical engineer and inventor in Britain, and his wife Janina, who survived deportation from Poland to Siberia as a girl before making her way to England.

Seven years ago, the couple sold off a rich portfolio of real estate they had acquired around Europe, liquidated their three corporations and even disposed of some of their jewelry so they could begin acquiring their collection for Poland. By the time they finished last year, they had purchased nearly 400 paintings, including works from almost every important European school from the 15th century to the 19th.

Jubilant Polish critics say the Pope John Paul II Collection, as the Porczynskis named the gift, represents a rare and precious acquisition by a country that has seen most of its stores of European art destroyed or stolen by occupying powers over the last century.

"The cultural balance for us for the last two hundred years has been one of constant loss because of occupations and uprisings," said Andrzej Przekazinski, director of the archdiocese museum. "This is the first event that changes that situation -- the first time that we are getting, rather than losing, a part of the European heritage."

The collection also has sharpened a growing rivalry between church and state in the sphere of culture. Since 1981, when the imposition of martial law by the government of Gen. Wojciech Jaruzelski caused a large number of artists, writers and actors to abandon official posts and forums, the church has enjoyed growing prestige as an alternative cultural sponsor. Its role has been particularly important in painting and sculpture because of its ability to provide artists with sites to stage independent and uncensored exhibitions.

Art critics say the rich new store of paintings, which in many ways is superior to that of Warsaw's national museum, will help consolidate the church's position and give it an important place in the education of both artists and the public.

"A lot of people who have never been exposed to the art world will now come to see the European paintings and will encounter our modern Polish art alongside it," said Alexander Wojciechowski, a prominent art critic. "Artists will want to reach that new audience through the church."

Government officials deny any resentment of the church's acquisition, but a subtle struggle between church and state over the collection is already underway. Because the five small rooms of the archdiocese museum cannot properly accommodate the paintings, church officials have sought state permission to build an entirely new museum to house the collection, along with preservation workshops, art classrooms and studios.

While not openly rejecting the church request, Jaruzelski's government has responded with an offer that the collection be housed in a recently restored state-owned palace dating from the 18th century. "It's not quite a question of rivalry," said Wojciechowski, "but clearly the state would like to bring the collection on its property and thus have a say in managing it. And that's unacceptable for the church."

While the standoff continues, the church has organized an exhibition of its new treasures in three stages. The first show of 160 paintings, mostly from the Renaissance and early baroque eras, opened in early November and has been besieged by spectators who line up outside the museum's heavy wooden doors for hours.

Crammed inside below low arched ceilings, along the walls of a stairwell and in hallways is a concentration of work by European masters unavailable at any other Polish museum: Rubens' "Flight Into Egypt," Van Dyck's "Portrait of a Nobleman," Titian's "Death of Lucretia," self-portraits by Rembrandt and Velasquez and works attributed to Tintoretto, Correggio and Cranach among others. Waiting to be shown in subsequent exhibitions are works by Gainsborough, Goya, Du rer, van Gogh and Renoir.

In a text recounting their art collecting, the Porczynskis said they were able to purchase the majority of the works in 1982 and 1983, when prices were relatively depressed. Since then, the boom in art prices has sent the value of the collection soaring, although church officials are unwilling to estimate its overall worth.

"The importance of the collection is that it is so full and broad," said Danuta Wroblewska, one of the museum's curators. "We are talking about a review of European painting over 500 years in which almost every school is represented. That has great value in a country like Poland, without many great collections, and it is of great educational value for young painters and the public at large."

Many of the paintings are religious scenes, as the Porczynskis' original intention was to acquire only works related to biblical themes. In time, however, the couple also came to specialize in portraits and self-portraits by major artists. Wroblewska said the portrait group, with its works by Velasquez, Rembrandt and van Dyke, is arguably the strongest part of the collection.

For museum director Przekazinski, the greatest significance of the collection is in the moral boost it has given Polish society. "In the economic crisis like we have in Poland, where we hear so much about the debts we owe abroad, this gift reminds us that everything is possible, and that we are not alone in the world," he said.

"It really helps people psychologically by telling them we are still connected to European culture and the great European traditions. Only here could it have that special value."