A coalition of national religious groups has unveiled plans for a network of financial and legal support for refugees in this country from El Salvador and other embattled Central American nations.

Mary Solberg, a member of the Lutheran Immigration and Refugee Service in New York, said some coalition members would offer undocumented immigrants sanctuary in churches, would provide them with legal and immigration counseling and would lobby the Reagan administration to halt their deportation from the United States.

Spokesman for the coalition said the refugee problem had reached crisis proportions, and they estimated there are 250,000 Salvadoran refugees in this country. El Salvador has been in the throes of civil war for two years.

Other components of the plan include the establishment of a national bail-bond program for the illegals and funding of a national toll-free telephone number that refugees could call for assistance and advice. Church leaders also will buy stock in airlines that contract with the federal government to return the immigrants to their homelands, Solberg said, and lobby the airlines--as stockholders--to stop the practice.

She also criticized Immigration and Naturalization Service officials for closing refugee deportation proceedings to the public, and accused the INS of denying the refugees legal information and coercing them to make voluntary departure statements that were later used against them.

A recent study by a United Nations group found the United States in apparent violation of U.N. protocol on refugees. The study said Salvadorans were routinely denied asylum and deported, and that in some cases the refugees were not made aware of their rights to seek political asylum.

William K. Gilligan, an INS officer in San Pedro, Calif., took issue with claims that illegal immigrants are being denied legal advice or coerced into making departure statements. He said many choose to make voluntary statements to avoid deportation and subsequent possible felony action if they are caught illegally entering this country. He also said the immigrants are granted "free legal services" but if they refuse it, INS will not provide lists of private attorneys because of the cost.

Solberg called on the INS to allow human rights representatives to monitor refugee detention conditions. Her statements came as Sen. Dennis DeConcini (D-Ariz.) announced he is seeking a federal investigation of a federal alien detention camp in El Centro, Calif.

El Centro is a desert community located midway between San Diego and Phoenix. DeConcini staff members said they were left "in a state of shock" after a tour of the camp last year.

Gilligan said many of the criticisms voiced by the staff members resulted from misconceptions. INS was criticized, for example, for not providing the refugees with adequate medical care. But Gilligan said a full-time nurse is stationed at the El Centro facility. More serious cases routinely are referred to physicians, he added.

Solberg said 32 organizations belong to the new coalition, including members of Catholic, Quaker, Presbyterian, Episcopalian and Baptist groups. Some Canadian organizations are included, as are refugee service groups in Los Angeles, Seattle and Dallas.