In 1971, Daniel A. Manion, now a federal appeals court nominee, joined his father on "The Manion Forum," a syndicated program broadcast by hundreds of radio and television stations.

Manion's father, Clarence, began: "Dan, what are the things that you have observed which make you suspicious of the supremacy of the Supreme Court?"

"It seems to have gone into regulating schools and their management," Daniel Manion said. "It tries to redistrict the legislature, such as they're doing here in Indiana . . . . And they took prayer out of public schools . . . . And now it seems that they've allowed pornography both on the newsstands and in the movie theaters. That's why. Why is it supreme? Why are they allowed to do this?"

When his father suggested that Congress strip the Supreme Court of the right to review obscenity cases, Daniel Manion replied: "I'm glad there is a way we can curtail the Supreme Court."

If Manion, 44, is confirmed by the Senate, the lawyer from South Bend, Ind., will ascend to the court one level below the Supreme Court. But Senate Democrats are determined to stop the nomination in the Judiciary Committee Thursday, saying his views are too extreme to allow him to sit on the 7th Circuit Court of Appeals in Chicago.

In a "Dear Colleague" letter yesterday, committee Democrats Joseph R. Biden Jr. (Del.), Edward M. Kennedy (Mass.), Paul Simon (Ill.), Howard M. Metzenbaum (Ohio) and Patrick J. Leahy (Vt.) said they oppose Manion because he has an "undistinguished legal career" and "cavalierly disregarded his oath of office to uphold the Constitution."

They cited Manion's 1981 cosponsorship of a bill in the Indiana legislature to allow posting the Ten Commandments in public schools, although the Supreme Court two months earlier had ruled that unconstitutional.

Thursday's scheduled vote could be a turning point in the continuing battle over President Reagan's effort to reshape the judiciary. Although Reagan has named more than one-third of the nation's federal judges, the Democrats have refrained from challenging any nominee explicitly on grounds of being too conservative, focusing instead on questions of temperament and personal conduct. But the Manion nomination is a flat-out fight over ideology.

Manion, a one-term state senator, said that, whatever his personal views, "the bottom line is I have great respect for the Constitution." In Senate testimony, he made no apology for his controversial statements on his father's broadcasts and elsewhere but said he could not recall some of the remarks or that his suggestions were no longer practical. Although he has criticized Supreme Court rulings, Manion said, he would follow court precedents and not his own ideology.

Manion, a deputy attorney general in Indiana in the early 1970s, enjoys strong support among Republicans. Sen. Dan Quayle (R-Ind.), who attended Indiana University Law School with Manion, said he "epitomizes what we all like to see in jurisprudence."

Judiciary Committee Chairman Strom Thurmond (R-S.C.), who appeared on "The Manion Forum" in 1965 to denounce antiwar demonstrators, called Manion's father "a wonderful man" and his son "an able lawyer." Sen. Jeremiah Denton (R-Ala.) praised the nominee and said the elder Manion was "one of the most admired men in my life."

Manion's career has been closely entwined with that of his father, a longtime John Birch Society leader who died in 1979 at age 83. Clarence Manion, dean of Notre Dame Law School from 1941 to 1952, was later fired from a federal commission by President Dwight D. Eisenhower, whose administration he accused of "creeping socialism."

In 1954, he founded The Manion Forum, a conservative advocacy group that produced syndicated broadcasts and newsletters. Daniel Manion became a forum trustee in 1972 and often appeared on the broadcasts.

"Dan has lived in his father's shadow," said one liberal legal observer in Indianapolis. "He espouses most of the things his father espoused, but he does not have a particularly outstanding reputation as a lawyer."

People for the American Way, a liberal lobbying group, is using the forum's transcripts and correspondence against the nominee. In a 1973 fund-raising letter, Daniel Manion said: "Recently we uncovered a nationwide plan by the radical left to force conservative-oriented commentators off the air. The communists, through their various front groups, have systematically harassed radio and TV stations in an effort to have conservative programs canceled."

In a 1971 broadcast, Manion accused some antiwar protesters of "advocating communism." He asked why they were "allowed to run free" and said he hoped that "there will be some chance of getting them penned up."

The same year, as national treasurer of Young Americans for Freedom, Manion asked the group to help distribute his father's book, which contended that the Supreme Court has erred in extending constitutional protections to the states.

In his South Bend practice, Manion has handled mainly personal and commercial claims in state court. Critics note that he has published no legal articles, has never been the lead attorney in a federal court case and has never appeared in the 7th Circuit appeals court.

"He's not achieved anything of any particular significance," said Michael Gradison, director of the American Civil Liberties Union's Indiana chapter. "He's had a fairly low profile, except for his name."

The Chicago Council of Lawyers has opposed Manion for his "low level of competency," citing a legal brief that contained numerous grammatical and spelling errors, including utility as "utillity" and definitely as "definately."

The American Bar Association gave him a "qualified" rating, its lowest passing grade, with a minority calling him not qualified. Manion attributed this to his small-town practice and the fact that he is not an ABA member.

At his confirmation hearing last week, Manion said the Ten Commandments bill was a protest against the Supreme Court.

While he has criticized court rulings that apply key parts of the Bill of Rights to the states, Manion said it was now too widely accepted to be changed. He said he could not offer an opinion on the John Birch Society because he does not know its policies.

Forum documents, however, show Manion interviewing and praising the late congressman and John Birch Society leader Lawrence P. McDonald (D-Ga.). In 1979, he praised John Birch members for being "on the front line of the fight for constitutional freedom."

In a letter the same year to Equal Rights Amendment opponent Phyllis Schlafly, he said: "I will be so glad when the ERA is finally dead. The so-called Women's Movement has no cohesive force other than that stupid battle cry."

And in a 1979 note to a South Bend pastor, Manion said his father "fought for prayer in school and for the recognition of God in all public places. That was the basis of our Constitution and Declaration of Independence . . . . "