In an effort to court voter support in the 1984 election, President Reagan is visibly stepping up promotion of his social and religious agenda. How determined Mr. Reagan is to push this agenda if he wins a second term is a matter of conjecture. But a host of recent actions indicates he is starting to build as broad a coalition as he can among middle-America constituencies, including Roman Catholics, evangelicals, and other religious and ethnic groups. Among these actions:
* In the State of the Union message, the President renewed his appeal for an invigoration of ''traditional values.''
* His proposed budget for 1985 again calls for tuition-tax credits for parents sending children to parochial and other private schools.
* In an address to the National Religious Broadcasters convention this week, Reagan delivered his most impassioned speech to date on behalf of a constitutional ban on abortion.
* In this legislative session, he is pressing for a constitutional amendment to permit voluntary prayer in the schools. Senate majority leader Howard H. Baker Jr. (R) of Tennessee intends to make this the first piece of administration-sponsored legislation to be put on the Senate floor, according to an aide.
* The Senate is considering the President's appointment of California land developer William Wilson to be United States ambassador to the Holy See as well as the question of providing funds for expanding the US mission at the Vatican.
Not all denominational groups are pleased by Reagan's use of his presidential office to promote objectives that touch on controversial questions of religious freedom. In fact, some sectarian groups favor one issue, such as prayer in the schools, but not others such as tuition-tax credits. Some support an anti-abortion amendment but not US diplomatic recognition of the Holy See.
Mainline Protestant groups, in particular, are concerned about what they see as a growing trend in the White House to promote sectarian values not shared by all Americans and to breach the constitutional principle of separation of church and state.
Immediate concern centers on the Vatican issue. After quietly promoting congressional legislation that freed the President's hands to establish formal diplomatic ties with the Holy See, the administration now seeks to provide funds for upgrading the US mission at the Vatican. Sen. Paul Laxalt (R) of Nevada, a close adviser of the President, has given preliminary approval to the State Department's request to use $351,000 of its undesignated funds for this purpose. He has done so in his capacity as chairman of the Senate Appropriations state and justice subcommittee. The House, for its part, takes up the funding question in an Appropriations subcomittee on Feb. 9.
Resistance to the Vatican move appears to be burgeoning, however. Members of Congress are beginning to look at the issue more closely as calls and letters are received from constituents. During the recent congressional recess, the House Appropriations judiciary subcommittee received more calls about the Vatican appointment than any other matter, according to a subcommittee aide.
Meanwhile, Sens. Mark O. Hatfield (R) of Oregon and Lowell P. Weicker Jr. (R) of Connecticut planned to send a letter to Mr. Laxalt Thursday expressing concern about approval of the State Department funding request and asking for a meeting of the Appropriations subcommittee to consider the issue. Senator Hatfield, chairman of the full Senate Appropriations Committee, opposes upgrading US relations with the Vatican on constitutional grounds.
Protestant church leaders are especially disturbed about the unpublicized way in which the administration appears to be maneuvering the Vatican appointment through Congress. Church spokesmen say the Senate Foreign Relations Committee hearing on the Vatican appointment was scheduled for Feb. 2 very hastily and without due public notice. Learning of the hearing, various groups quickly requested time to participate. The American Jewish Congress, a spokesman says, wanted to testify against the appointment but did not have anyone available to do so on such short notice.
''It's a back-door approach,'' says a spokesman for Americans United for Separation of Church and State (AU), a lobbying group that opposes full ties with the Vatican. ''They're doing it as fast as they can. They want to keep us off balance.''
According to a committee aide, the hearing was scheduled by Sen. Richard G. Lugar (R) of Indiana, who sponsored the Vatican legislation passed by Congress. Mr. Lugar, who heads the Republican senatorial committee, also chaired the confirmation hearing.
''All this points to complicity with the White House,'' says one church official.
Aside from the Vatican issue, there is growing unease in some denominational quarters over the President's fervent catering to fundamentalist religious groups and his use of excessive rhetoric. In his speech to the National Religious Broadcasters (NRB) Monday, Reagan frequently invoked the Bible, declaring at the end:
''If the Lord is our light, our strength and our salvation, whom shall we fear? Of whom shall we be afraid? No matter where we live, we have a promise that can make all the difference, a promise from Jesus to soothe our sorrows, heal our hearts, and drive away our fears. He promised there will never be a dark night that does not end. Our weeping may endure for a night, but joy cometh in the morning. He promised if our hearts are true, his love will be as sure as sunlight. And, by dying for us, Jesus showed how far our love should be ready to go: All the way.''
Many religious leaders view such rhetorical flourish as simply part of the traditional pattern of presidential electioneering. ''Every single president except John Kennedy has done the same thing,'' comments Rabbi Marc Tannenbaum of the American Jewish Committee. ''Presidents aim for every ethnic and religious group in America, tailoring their appeal to elicit support from various specialized constituencies.''
''He needs to reestablish his bona fides with an important element of his constituency,'' remarks Dean Kelley, an official of the National Council of Churches. ''A number of the evangelicals are out of patience with him. He's not expending a lot of political capital on them.''
Other religious and civic groups say they believe President Reagan has gone well beyond an acceptable level of politicking in courting the evangelical right. A spokesman of the Baptist Joint Committee calls the NRB speech ''the most blatant example of misuse of civil religion that any president has used. . . . It does Christianity a disservice.''
Comments the AU spokesman: ''Reagan does not seem to distinguish between his personal beliefs and what a president of a pluralistic country should say.''
It is uncertain how energetically the President would press his social agenda in a second term. It has not been a high priority during the past three years. Political experts say - inasmuch as Reagan would be a lame-duck president in a second term and in view of congressional opposition to tuition-tax credits and other items on the White House agenda - it is unlikely he could achieve his objectives. More probable, they say, he would count on being able to make one or two Supreme Court appointments to influence future decisions in a more conservative direction.
Among church groups, too, there is skepticism that Reagan, while he may be sincere in his views, is as committed to the social agenda as to his economic and defense programs. As one Protestant spokesman puts it, ''Religion is being used as a political commodity.''