The conservative movement has split into bitter factions over the issue of economic sanctions against South Africa, according to spokesmen for the combatants.

A group of younger conservative House Republicans, including Reps. Jack Kemp (N.Y.) and Vin Weber (Minn.), who consider themselves populists and ideological innovators have angered other conservatives by favoring sanctions against the white government of South Africa to demonstrate opposition to the policy of apartheid, or rigid racial segregation and white dominance.

At the same time, many right-wing groups and individuals strongly oppose sanctions against South Africa and hope that President Reagan will veto any bill from Congress that would impose them.

Some White House staff members who assume that Reagan will veto a sanctions bill have been pressuring pro-sanctions conservatives to correct what they perceive as an ideological error.

"Those of us who are critics [of South Africa] are coming under pressure," Weber said in an interview. "Conservatives in the White House want us to change our position."

Several involved in this fierce intratribal conflict said the issue goes beyond the specifics of how to deal with South Africa. They argue that the differences over sanctions reflect a more fundamental split over the future of the conservative movement and of the Republican Party. "There's a lot of wailing and gnashing of teeth," Weber observed.

Conservatives are trading insults among themselves of a kind usually uttered only by their opponents. "They're operating from a large base of ignorance," said Howard Phillips, president of the Conservative Caucus, about the pro-sanctions House conservatives. "Acute moral cowardice . . . intellectually dishonest . . . ill-informed," he added. A White House official described the pro-sanctions conservatives as "often politically naive. Sometimes they need education."

Several New Right leaders seemed especially angry at Kemp, whom many consider a natural conservative candidate for president. "Jack Kemp has badly damaged his presidential prospects by being to the left of George Bush on this issue," Phillips said. Kemp was traveling in Asia and could not be reached.

A Kemp ally in the House -- one of the younger conservatives who have banded together as the Conservative Opportunity Society (COS) -- called the position of the other conservatives "destructive," and said he was "shocked" by the Rev. Jerry Falwell's defense of the South African government. This House member suggested that the New Right's suddenly intense concern over the issue may be motivated by the need to raise money, and that it has chosen this emotional issue to try to replenish its depleted treasuries.

"You have to ask the question: What's the potential of the New Right raising money through direct mail? If they can develop an issue that will generate money they will move it to the forefront of their agenda," the COS member said.

The rift among conservatives first opened in December when 35 conservative House Republicans led by Weber, Rep. Newt Gingrich (Ga.) and Rep. Robert S. Walker (Pa.), signed a letter harshly critical of the South African apartheid policy and delivered it to the South African ambassador. "There is no ideological division in our minds in this country in our approach to the question of apartheid . . . . All Americans find it repugnant," they wrote.

They were immediately vilified by the conservative columnist Patrick J. Buchanan, who said on The McLaughlin Group television show taped Dec. 28 that the COS group was "turncoat of the year" for "stabbing South Africa in the back." A month later Buchanan had been named White House communications director.

When the House approved an economic sanctions bill by a 380-to-48 vote, the COS members joined the overwhelming majority. However, one early member of the Conservative Opportunity Society, Rep. Mark D. Siljander (R-Mich.), has abandoned the pro-sanctions position.

Weber said that South Africa raises "a genuine moral issue," but added that his support for sanctions also has a political dimension. "The appearance of tolerating [racism] has to be eliminated" if conservatives are ever to lead the Republican Party to a majority position in the country.

But New Right leaders like Phillips deny that support for South Africa's government is a racist position. "Instead of accepting that formulation, they should be pointing out its fraudulence," said Phillips. In his view, the South African government favors "reform" of apartheid and is "a target for destabilization by the Soviet Union."

New Right groups have moved quickly to mobilize against sanctions. The Conservative Caucus led by Phillips, for example, prepared a huge mailing to potential donors, and Falwell's Moral Majority launched a $1 million drive to block sanctions.

Early this week, many New Right leaders met in Buchanan's White House office to discuss strategy, according to conservative sources.

The White House Office of Public Liaison, directed by Linda Chavez, began mobilizing conservative support against sanctions. She privately advised the New Right groups on the public presentation of their case, urging that they emphasize their opposition to apartheid, according to a White House source. Her executive assistant, Don Eberle, a longtime conservative activist, began lobbying COS members to change their position. "He's not acting in any official capacity," said Chavez. "That's not part of his responsibility."

"The demagogues have the high ground," said Burton Yale Pines, a vice president at the conservative Heritage Foundation, which sent a representative to the meeting in Buchanan's office. As a result of the COS adamancy on the issue, "You're a racist if you don't bludgeon apartheid with a sledge hammer," Pines said.

The conflict among conservative leaders "confuses a lot of the constituency out there, including the financial constituency, conservatives who have begun to see COS as part of the conservative movement for which they are writing checks," Pines said. "You're going to have to sit these people down and explain to them what's happened."