In a dramatic clash of church and state, the Roman Catholic Church and the Reagan administration took starkly opposing views on Capitol Hill yesterday about the growing U.S. military role in El Salvador.

Washington Archbishop James A. Hickey, testifying on behalf of the Catholic hierachy in the United States before a tense and crowded hearing, strongly opposed military aid to Ed Salvador and called the introduction of additional U.S. military advisers "risky to the point of being reckless."

He told the House Foreign Affairs subcommittee on inter-American affairs that the additional U.S. military presence, announced Monday, "confirms the worst suspicions of Latin Americans that we are slowly preparing for an invasion of El Salvador."

Military aid, he added, associates the United States with "still uncontrolled" Salvadoran security forces, which have been accussed of large-scale murders and atrocities, including the killing of four American women missionaries in December. Two of the dead nuns had been assigned to El Salvador by Hickey.

Hickey urged the U.S. government yesterday to shift its course toward greater political and economic efforts. He called for Washington to use political rather than military pressures against the flow of outside arms to Salvadoran insurgents and to encourage actively an internal political dialogue between government and leftist forces rather than continuing "a notable silence" on such a political solution.

Testifying for the Reagan administration, John A. Bushnell, acting assistant secretary of state for inter-American affairs, depicted the Salvadoran conflict in international strategic terms that require a U.S. response. Bushnell said El Salvador is "merely a subset of much larger problems," charging that "the world communist network intervened in El Salvador . . . from all over the world . . . to add another country to the communist bloc."

Bushnell argued that the sending of additional U.S. military personnel need not be reported officially to Congress under the War Powers Resolution because most of the personnel will be in relatively safe Salvadoran army camps. At the same time, he suggested that their peril has been intensified by the controversy in this country, which has given high visibility to a small number of American military -- about 25 currently, soon to be augumented by about 20 more.

It must be "tempting" to the forces of both the right and the left in El Salvador, Bushnell testified, "to think they might win their struggle in Washington, to traumatize this country, by going after Americans who happen to be in El Salvador." He said that shots fired against the U.S. Embassy in San Salvador Wednesday might have had such a political purpose.

With greater frankness than has been displayed in earlier State Department pronouncements, Bushnell said the United States faces "somewhat of a dilemna" in its stand on political solutions to the Salvadoran conflict. "We can't go into this situation with both hands tied behind our backs," he said, indicating that pressure for a peaceful settlement could undercut U.S.-backed forces without affecting Marxist groups determined to take power "at the end of a gun."

Bushnell refused to speculate on what the United States will do if the current and projected levels of military and economic aid and political pressure do not stabilize the situation. However, he spoke repeatedly of "very favorable signs" that the level of outside arms to the Salvadoran guerrillas has diminished recently and may have stopped.

Rep. Gerry E. Studds (D-Mass.), who recently returned from the area with strong doubts about U.S. policy, commented after hearing Hickey and Bushnell that "one of the traditionally conservative of institutions, the Catholic church, and one of the originally most revolutionary of institutions, the United States of America, appear to have passed in the night" in Central America, reversing their earlier roles.

The El Salvadoran controversy has energized Roman Catholics in the United States as have few other political issues in recent times. Prayer vigils and letter-writing campaigns have sprung up among Catholics across the country, and church leaders have been calling on political leaders. The church, at considerable political risk, is taking an ever-stronger posture against a U.S. military role just as the Reagan administration increases such activity.

A few minutes before yesterday's hearing began, subcommittee chairman Michael D. Barnes (D-Md.) telephoned Salvadoran President Jose Napoleon Durate. According to Barnes, Duarte said he had amended an originally "unacceptable" plan for U.S. military aid presented to him by the Salvadoran military. Bushnell confirmed during his testimony that Duarte "cut down" the original Salvadoran military aid request.