Irene Jarosewich, a public relations executive in Washington, labored over her computer three days this week, writing a statement timed for the summit that urged U.S. support for legalizing the Ukrainian Catholic Church.

No stranger to Washington politics, she knew that her missive would be only one of hundreds of individual pleas landing at the State Department. But she worked at a pace intense even for this city, moved by the memories of a recent visit to the western Ukraine where she witnessed 8,000 Catholics worshiping outside a locked cathedral.

Jarosewich is one member of an increasingly vocal lobby of U.S. believers who, emboldened by a measure of openness in Soviet religious life, are sending millions of dollars and Bibles to the Soviet people and demanding broader religious freedom in that country. People of like mind are attending freedom rallies around the city this week and at the Washington Cathedral, site of a summit-long prayer vigil.

Public attention to religion in the Soviet Union, once confined to the plight of Soviet Jews, has broadened in recent months as Americans have learned how spiritual the Soviet people are -- about 100 million are said to be believers of an estimated 287 million population -- and how important religion has been in keeping that country's various national cultures alive.

Since Stalin outlawed religious activity in 1929, church rituals regularly have been celebrated in secret, and underground church newspapers have documented Soviet repression.

Religion "sustained the people's dignity in the face of an incredibly brutal system," said Jarosewich, 33, the American daughter of Ukrainian parents.

Said Archbishop Kirill Gundiaev, a top official in the Russian Orthodox Church in Washington during the summit: "The church was the school of pluralism in an otherwise monochromatic, monolithic state. Despite attempts to annihilate it, its existence prepared the way for the many faces of perestroika, including nationalism."

The presence here of the Russian archbishop, as well as Armenian Apostolic, Baptist and Lutheran bishops in his delegation, is an indication of major changes taking place in Soviet religious life. Reform has been particularly evident in the Baltic and western republics, partly because those regions have had closer ties to the West and some access to Western assistance.

The Soviet government has reopened about 2,000 churches in two years. Christian and Moslem clergy once considered dangerous now appear regularly on Soviet radio and television. Religious institutions, previously banned from participating in charitable work, are now encouraged, and church-run soup kitchens have sprung up in several cities. In Lithuania last year, elective courses in religion were introduced in public schools.

Religious leaders have been elected to the Soviet legislature and to the Moscow city council. Some of those leaders emerged from the country's intelligentsia, which, according to various Soviet analysts, is no longer predominantly atheistic or indifferent to faith in God.

"In the 16 years preceding the millennium of Russia's official Christianization {1988}, over 30 million souls were baptized into the Russian Orthodox Church of whom most, at least in the major urban centers, were adult converts, largely intellectuals," said Dimitry Pospielovsky, a historian of Soviet church-state relations at the University of Western Ontario in London, Canada.

Gorbachev, Pospielovsky said, is the first Soviet leader to recognize that the church can be a powerful ally in winning popular support for needed economic reforms.

Reportedly baptized as a child, the Soviet president has made several gestures indicating his interest, including opening the Kremlin to religious leaders during millennium celebrations. "It's worth {Gorbachev's} while to mobilize religions to keep the people in order," said Yaacov Ro'i, a visiting professor of Russian history at Georgetown University.

Ro'i, who sees a rise in religiosity among virtually all Soviet populations, says Gorbachev hopes that trend will begin to chip away at the country's severe crime, alcoholism and drug problems. Gorbachev has brought religious leaders into his orbit at some risk: He may be able to defuse their nationalist tendencies, or he may embolden them to push their flocks further toward independence.

Religion lobbyists are working this week to make Americans understand that despite Gorbachev-inspired reforms, the Soviet faithful still face enormous obstacles in their religious life. One hurdle is the Stalin-era legislation that remains in effect.

Reports of persecution still surface in the rural areas. Church buildings, previously used for everything from breweries to museums, are in horrible condition and the clergy have no money to repair them. Religious education classes have little or no literature. The most profound problem, however, may be internal divisions inspired by years of repression: suspicion of the Orthodox faithful toward the church hierarchy, and competition between various religions for resources.

American churches, seeing these needs as well as an opportunity for evangelization, have responded. The U.S. Catholic Conference, the national body of Roman Catholic bishops, is setting up a four-person office in Washington to help with books, seminaries and social service programs in the Soviet Union. The Southern Baptist Convention, the country's largest Protestant denomination, recently appropriated $1 million in aid and assigned its first full-time missionary couple to Moscow.

The American Bible Society, a multi-denominational group, sent 1.7 million Bibles to the Soviet Union this past year, and hopes to send 30 million more by 1994.

Other organizations are trying to make political contributions. "The guarantor of religious freedom will be independence," said Victor Nakas, of the Lithuanian Information Service. His organization used to report solely on religious news but, aided by a surge in U.S. donations, has expanded to cover the independence movement.