Los Angeles — For five weeks this fall, the Rev. Ronald B. Halvorson had a booth set up in the lobby of his church to pass out voter registration forms. Along with the forms came pamphlets crisply rating both state and national candidates on ''Biblical'' issues - among them abortion, the Equal Rights Amendment, prayer in public schools, the nuclear freeze, and a balanced federal budget.
About 400 members of Dr. Halvorson's congregation at Bethel Christian Center in Riverside, Calif., filled out registration forms this year, roughly triple the number in 1980.
Because of the pamphlets, says Dr. Halvorson, ''I would think ... people are taking a more definite stand.''
The religious right - conservative Protestant Christians who are fundamentalist both in their religion and their Americanism - is emerging as perhaps the best-organized, most monolithic major voting bloc in modern politics.
Through churches like Dr. Halvorson's, and others involved in election-day, get-out-the-vote phone drives, the religious right hopes to bring between 5 and 6 million more Christians to the polls today than voted in 1980. It claims to have registered nearly 2 million new fundamentalist voters this fall.
Unlike many conservative Protestant pastors, Dr. Halvorson has always encouraged his congregation to take part in the nation's political life. But, he adds, ''I've never had help before.''
The help this year comes from the American Coalition for Traditional Values (ACTV), the grass-roots political organizing arm of the religious right. ACTV - pronounced ''active'' - is headed by television evangelist Tim LaHaye in San Diego. It includes the Moral Majority, Christian Voice, and similar groups.
The coalition has worked to build a network of fundamentalist political activists keyed to areas with races deemed important to furthering traditional values.
Bethel Christian Center, for example, is in the congressional district of Rep. George Brown Jr., a liberal Democrat who scores poorly on ACTV's ''Biblical score card.'' Although he is a Methodist with a base of support among mainline Protestants, Mr. Brown's positions run counter to what ACTV designates to be the Christian positions on the whole gamut of cultural and national defense issues.
A smattering of Democrats across the country, mostly in local races, have ACTV support, but its blessings fall overwhelmingly to Republicans. President Reagan has the unqualified support of the movement.
Bill Roberts, a political consultant to the Reagan campaign nationally and longtime Republican strategist in California, estimates that the religious right carries the direct impact of about 5 million voters across the country - a much tamer estimate than comes from the ACTV itself.
The real size of this fundamentalist monolith is a little vague. Albert J. Menendez, research director at Americans United for the Separation of Church and State, estimates from polling data that conservative white Protestants make up at least 20 percent of the electorate, or about 20 million people.
Richard Pierard, a professor of history at Indiana State University, puts the ''hard core'' constituency of the religious right at 5 million to 8 million. A larger group of evangelicals, he says, doesn't take much interest in politics, yet is susceptible to the emotional appeals organizations like the Moral Majority make on behalf of beleaguered traditional values.
Political activism is a relatively new movement among conservative Protestants, a group that historically has voted less than any other major religious category. They tend to be older, poorer, and more predominantly female than the rest of the electorate. The other reason is that conservative Protestants lost the political battle in the 1920s with liberal Protestant activists and turned inward, concentrating on individual salvation.
Lou Sheldon, ACTV organizer in the Los Angeles area and chairman of the California branch, finds that only about a quarter of the conservative Protestant ministers he approaches are ready to take an active church role in politics. The others, he says, are ''still a little intimidated by the Big Lie, '' which he says is the notion that there should be a wall of separation between church and state. The US, he asserts, was founded as a ''Christian republic'' from the outset, based on Judeo-Christian, biblical values.
The call of the religious right is to fight for Christian, family-oriented, traditional morality against the onslaught of ''secular humanism.'' The issues the movement has flagged: banning abortion, fighting full civil rights for homosexuals, restricting pornography, bringing voluntary school prayer back to public schools, fighting the Equal Rights Amendment for women, strengthening the military, defeating the nuclear freeze, promoting capital punishment, and amending the Constitution to require a balanced federal budget.
''These issues,'' says Professor Pierard, a Baptist, ''are no more biblical than the man-in-the-moon.'' Rather, he says, the movement goes back to turn-of-the-century fundamentalists who were attempting to preserve a 19 th-century way of life. ''They don't like social change, cultural change,'' says Mr. Menendez. ''They've concocted a new devil - humanism. It's a new McCarthyism , moral McCarthyism.''
From the other side, Curtis Maynard, manager of ACTV's San Diego office, says: ''We just feel there needs to be more of a balance.''
The Presidential Biblical Scoreboard, a publication of the Biblical News Service which rates candidates on ''Biblical, family, moral issues,'' asks: ''Do you know what we could do with 30 million Christian votes? We could elect a president no matter how objectionable he was to the liberal, humanist media; we could ensure that a majority of congressmen took a strong moral stand; and we could pass Godly legislation.''