Elliott Abrams, assistant secretary of state for inter-American affairs, says he doesn't expect to be having lunch with Sen. Jesse Helms (R-N.C.) anytime soon. Only last week, the two men traded charges about "indefensible" conduct in U.S. dealings with Chile. Still, Abrams says he believes that Helms inadvertently performed a valuable service for the Reagan administration by "allowing us to clarify our commitment to a return to democracy in Chile."

The disagreement began when the North Carolina senator, who was visiting Santiago, harshly criticized U.S. Ambassador Harry G. Barnes Jr. for attending the funeral of a young Chilean (a District of Columbia resident) who died after police allegedly set him afire during an antigovernment demonstration. Abrams immediately told the Associated Press that Helms' remarks were "indefensible" and charged that "those who support an indefinite extension of military rule in Chile are playing into the hands of the communists."

"Before that, we were locked into a position of reacting to events in Chile," Abrams said in an interview. "Now, because of Helms' attack, we have had an opportunity to make our position clear to the American public and to the Chilean government. The fact that Helms seems completely isolated -- that no one has supported him -- has underscored to the Chileans that there is a broad consensus among American conservatives about the need for a transition to democracy."

The relish with which Abrams took on Helms, the doyen of Republican arch-conservatives in the Senate, reinforced his reputation as the State Department's resident "tough guy." There he is known as a man who rarely shrinks from using the most effective weapons at hand -- whether acid-tinged public rhetoric or backroom politicking -- to advance his fiercely held and usually controversial convictions.

As one of the architects of President Reagan's policy of support for the counterrevolutionary guerrillas, or contras, fighting Nicaragua's leftist Sandinista government, Abrams unblinkingly engineered the recent ouster of the U.S. ambassador in Honduras, John A. Ferch, because he felt that Ferch was not managing the contra aid program with sufficient vigor.

But on an earlier occasion involving Chile, he persuaded Secretary of State George P. Shultz to fire another U.S. ambassador regarded as too close to the military regime there. That gave Abrams, who regards himself as a staunch conservative, a reputation as a "radical" in right-wing circles. But he refused to waver from his conviction that efforts to coax the Chilean military toward liberalization were not working and that the U.S. interest required a gesture of displeasure.

Abrams proceeds from the premise that the world, as he once put it, is "an exceedingly dangerous place." He also contends that the principal source of danger is the Soviet Union and that countering Soviet threats requires different methods in different places. In his view, it is not inconsistent to engage in force through guerrilla proxies in Central America while pursuing a low-key emphasis on human rights in Chile.

"I am a conservative, and I view things from a conservative standpoint," he said. "I don't see any large differences between me and other conservatives. But if there are, they stem largely from the questions of where you came from and how you got to where you are."

That was an indirect reference to his reputation as a prominent member of the neoconservative movement. The label, while subject to debate, generally is applied to former Democratic liberals who, believing that the liberalism of the New Deal and Fair Deal has exhausted its effectiveness or been perverted by newer trends in the party, have shifted their allegiance.

In those circles, no one has credentials more gilt-edged than Abrams. He is a member by marriage of neoconservatism's closest equivalent to a royal family, and his concepts of national interest and public service were forged in an informal finishing school of neoconservative ideas.

His wife, Rachel, is a daughter of Midge Decter, a writer who is among the most articulate exponents of neoconservative views. Rachel's stepfather, Norman Podhoretz, is a prolific writer and the editor of Commentary, the journal published under the auspices of the American Jewish Committee that is the principal sounding board for the movement's most prominent members.

Abrams' association with the disaffected Democrats began during his days at Harvard Law School, when he lived in an attic apartment in the home of Nathan Glazer, a Harvard professor whose article several years ago in Commentary on the limits of governmental intervention is regarded by many as the wellspring of neoconservative thinking.

Abrams' subsequent introduction to government service came as an aide to the two Democratic senators -- the late Henry M. Jackson of Washington and Daniel Patrick Moynihan of New York -- who were once regarded as the standard-bearers of neoconservativism within the Democratic Party.

It was from that background that Abrams in 1981 became, at age 33, the youngest person to hold a State Department assistant secretary post in this century. Now, 6 1/2 years after Reagan became president, Abrams and Chester A. Crocker, assistant secretary for African affairs, are the only original Reagan appointees at State still holding senior policy-making positions in the department.

Abrams started as assistant secretary for international organization affairs. But his emergence as a force in administration foreign policy began a few months later when he was shifted to the post of assistant secretary for human rights after Senate opposition caused Reagan's original choice, Ernest Lefever, to withdraw.

Many observers, recalling Reagan's attacks on the activist human rights policy of the Carter administration, suspected that Abrams was being called on to dismantle the program. But as Aryeh Neier, one of the country's most prominent rights activists, points out, what happened under Abrams' leadership was an evolution into a different but clearly discernible approach to human rights issues.

It meant that for almost five years Abrams had to walk a tightrope between suspicious liberals, wedded to the Carter-era approach, and the Republican far right, which has never surrendered its determination to eliminate the human rights program. In Abrams' terms, that meant fighting to ensure that Reagan's advocacy of "quiet diplomacy" didn't become an excuse for doing nothing, and using it instead as a springboard for resolving individual cases of rights abuses, applying pressures in cases such as Chile where persuasion didn't work, and emphasizing the virtues of democracy over dictatorship.

It fell far short of what the activists wanted. But it impressed Reagan and Shultz, who decided last year to move Abrams to the department's Latin America bureau and give him the job of day-to-day management of the administration's controversial Central America policy.

Once again, liberal critics of the administration haven't been overjoyed by his performance. But even those who dislike his hard-line approach to Nicaragua acknowledge that Abrams has been effective in resolving differences that previously put State at odds with other agencies in the foreign policy apparatus.

Where the State Department earlier was perceived as lukewarm toward the contras, Abrams, with Shultz's backing, helped to make clear that the administration is united behind the strategy of using the contras to pressure the Sandinistas. Now that Reagan's battle to win $100 million in contra aid from Congress appears on the verge of success, Abrams will have most of the operational responsibility for proving the administration's contention that the strategy will work.

But he denied that the primacy of the contra strategy is proof that the administration is determined to overthrow the Nicaraguan government. Referring to the Contadora talks among Central American countries and other Latin states, he said:

"Until now, many of the participants were interested in getting an agreement that would be unacceptable to the United States because it would give Nicaragua a blank check for subversion in the region or in using the negotiations as a way to defeat contra aid in Congress. Now we're making clear that can't be done. When it's recognized that the contra pressure is going to be there until Nicaragua is willing to change its ways, we think that perhaps we might start to see a chance for negotiations that are meaningful.