On a snowy winter day last December, seven Catholic bishops and archbishops retreated to the Marriottsville Spiritual Center near Baltimore to launch an important religious mission.

They gathered as they do twice each year, seated comfortably in a spacious conference room overlooking the countryside. There, in their day-long seclusion, joined only by their communications director, attorney, and a legislative lobbyist, they plotted a comprehensive political agenda for the months ahead that would influence important legislation in the Maryland State House.

This clerical Board of Governors decided to urge welfare grant increases for the poor, a position that Maryland Gov. Harry Hughes later adopted in his budget message and that the General Assembly now has approved. They chose to oppose the "natural death act," which the House of Delegates defeated last week. They agreed to work for bills to help migrant farm workers on the Eastern Shore. And they concurred on pressuring for stiff procedures for divorce, more aid to foster children and an end to state-funded abortions and nuclear proliferation.

"Some who vigorously question our participation in public affairs suggest we stick to religious teaching and spiritual matters," said Washington Archbishop James A. Hickey, whose archdiocese includes the Maryland suburbs of Washington. "I maintain that speaking out for the poor and vulnerable is profoundly religious. In fact, it is required by our faith."

The bishops' retreat was just one of a series of steps by the Catholic Church to increase its involvement in Maryland politics, where it already is considered the most successful lobby supporting social welfare legislation. With the Vatican leading a world-wide crusade on social justice issues, church leaders increasingly emphasize their role in state politics -- and try to assuage fears that they are violating the American principle of separating Church and State.

"Our chief legislative commitment is a reflection of the Church's concern about the poor," said Hal Smith, director of Associated Catholic Charities, which operates more than 30 programs for the poor, elderly and displaced in Baltimore. "Increasing the welfare grant was our top priority because it is the one area that impacted in the broadest possible way on the people we serve."

To ensure that its views are heard in the General Assembly -- more than half of whose members are Catholic -- the church spends nearly $100,000 a year. It has become involved in a wide array of political issues and displays new political savvy in pushing for legislation in a state where roughly one-third of the five million citizens are Catholic. But it is in the area of social welfare, rather than on the traditional Catholic issues such as abortion where the church has tread lightly, that its lobby here has had the greatest impact.

More than before, high-ranking bishops have appeared in Annapolis to testify. Just two weeks ago, the Most Rev. P. Francis Murphy of the Baltimore archidiocese told a House committee it was "a moral imperative" to prevent the use of nuclear weapons. Another Baltimore bishop, the Most Rev. J. Francis Stafford, testified at another hearing to urge approval of welfare grants for expectant mothers.

"They the Catholic lobby always go on the record against abortion," explains Catholic Del. Gerard F. Devlin (D-Prince George's). "But they really work on welfare issues."

The growing clerical involvement has resulted in the hiring of three full-time lobbyists during the past five years and the creation of a church bureaucracy that deals specifically with public affairs. Other religious organizations -- such as those representing the Unitarian Church and Jewish organizations -- also have paid close attention to social legislation, particularly in the wake of President Reagan's budget cuts.

None has pressured as intensively for programs to help the poor as the two Catholic social action groups, The Maryland Catholic Conference, the 30-member legislative arm of the three regional archdioceses, and Associated Catholic Charities, a 60-year-old private, nonprofit social service agency affiliated with the Baltimore archdiocese.

In church lobbying, abortion has usually been linked with "defense of life" issues such as capital punishment. The church, however, always has moved cautiously on the volatile abortion issue, taking pains to disassociate itself from the tactics of right-wing fundamentalist groups such as the Family Protection Lobby that have dominated antiabortion lobbying here.

In fact, the two lobbyists for Catholic Charities, Cheryl D. Lynch and Andrew Carter, tend to skirt abortion legislation, principally because their organization does not take an active stand on it, but also because they do not want to jeopardize their alliances with other social justice groups that actively support legalized abortion.

They leave most bills involving the "defense of life" to Francis X. McIntyre, a former state superintendent for special education who now serves as lobbyist for the Maryland Catholic Conference and reports to the board of governors, which normally comprises all nine bishops and archbishops from Washington, Baltimore and Wilmington.

Operating out of a small second-floor office in the old YWCA building across from the State House, Lynch and Carter prepare fact sheets, position papers and an arsenal of statistics to deliver to legislators who might support their causes. Lynch, a veteran of five years of lobbying who also chairs one of four legislative committees that advise the Catholic Conference's governing body of bishops, has won respect in the 188-member legislature. She has forsaken, for the most part, the traditional lobbying techniques of wining-and-dining and has relied instead on sheer energy and grit and an intuitive understanding of the legislative process.

"They the church lobbyists are very effective," says House Speaker Benjamin L. Cardin (D-Baltimore), echoing a commonly held view. "They pick their issues and then they stick with them. Cheryl is probably the single most active lobbyist on social welfare issues. She has established a very good rapport with the legislature. She is a very good lobbyist."

Among Catholic Charities' successes in the past few years have been welfare grant increases, funding for child abuse and foster care services and expanded mental retardation programs. The organization has won to its side a number of unlikely supporters, including two influential legislators who are Catholics: Anne Arundel County Republican Sen. John A. Cade, who has become the leading proponent of increased welfare funding, and Sen. Francis X. Kelly (D-Carroll), a notorious fiscal conservative, who now is a prime backer of increased spending on shelters for the homeless and grants for pregnant women.

More recently, after nearly five hours of debate in a House committee, Lynch nursed through legislation to clarify the registration process for crew leaders that recruit migrant workers to Eastern Shore farms by working out a series of amendments that were approved on a final vote Friday night on the House floor.

"The bishops felt it was important enough that I should take the time and walk it through," she said of the issue that is of concern to the Most Rev. Thomas J. Mardaga, bishop of Wilmington, and the Rev. Arthur Gildea of the same diocese, who testified on the bill before the House Economic Matters committee.

McIntyre, too, has had victories, helping to defeat the "natural death act," which proponents called the "death with dignity" act, winning improvements in programs for the handicapped and limiting the instances in which the state will pay for abortions. His office is a single room in the St. Mary's parish near the State House. He says that, besides the annual meals hosted here by Washington Archbishop Hickey, Baltimore Archbishop William D. Borders and Mardaga of Wilmington, his expenditures on legislators this session have totalled four lunches and two dinners.

"There are different mystiques among lobbyists ," explains McIntyre, a bearded 45-year-old whose natty wardrobe includes three-piece pin-stripe suits, conservative ties, wing-tip shoes, watch chain and an always present pipe. "We have no axes to grind. We can't contribute to campaigns or buy tickets to fund-raisers. There are none of those quid pro quos. But I don't feel I have any less rapport with members of the General Assembly."

Picking the issues is usually a clear-cut process for the church lobbyists, because they focus mostly on purely social issues. They refrained from taking a position on a controversial measure to raise the ceilings on interest rates, despite arguments that raising those rates would hurt low-income borrowers.

Sometimes these decisions are not so easy. Lynch, for instance, has had to walk a thin line this year in pushing for legislation to restore funds cut by the Reagan administration for pregnant women on welfare. One provision in the bill calls for funds for "unborn children," language that did not sit well with feminist groups who connect the term to the antiabortion movement in Congress.

While most legislators, Catholic and non-Catholic, welcome the church lobby, others are skeptical about the power of Catholics in Maryland.There are still strong criticisms and prejudices," said McIntyre. "A vein of anti-Catholicism still exists."

"I have mixed feelings about their role," says Del. O. James Lighthizer (D-Anne Arundel), a Catholic. "Sometimes I think they overreach. I can see them being involved in fundamental moral issues, but not on ancillary ones. I listen to everything they say on moral issues, but not everything is a moral issue."

Beyond the church's political lobbying, which most legislators describe as "soft-sell," there is occasional resentment aired about the church's political influence and its sizable tax breaks for land holdings, educational facilities and charities. Liberals who applaud the energy and attention the church has paid to poverty issues often disapprove of its stand on abortion, divorce and birth control.

"The Catholic Church controls the divorce issue in this state," said one legislative staffer who asked not to be named, referring to the three-year time lag still required before a divorce becomes official in Maryland. "That, I believe, is religious objection."

Even the liberal critics usually show a grudging respect for the church's lobbying. "They pick up all the lost causes," said the legislative staff member. "If you look at the Crusades, well, you've got the same thing here. It's good, to the extent that it's always good to have a group that lobbies for the poor."