In the mid-1970s, a Central Intelligence Agency analyst named David S. Sullivan concluded that the Soviet Union had deceived the United States in negotiations leading to the 1972 SALT I agreement on strategic arms, and was doing the same in negotiations then taking place on the successor treaty known as SALT II.

Sullivan's activities in support of his thesis went beyond normal bureaucratic advocacy -- and beyond the level his superiors would tolerate. The husky ex-Marine, who still wears a military crew cut, has been fired from several policy-related Washington jobs. But the experience has not amended his views or diminished his intensity, and over time some of his ideas have become accepted U.S. policy.

The most important case in point is President Reagan's recent announcement of the end of U.S. adherence to the SALT II treaty, an action that Sullivan, a 43-year-old native of Philadelphia and son of an Air Force general, had advocated for years. How Sullivan played a role behind the scenes illustrates the clout -- and the perils -- of passionate advocacy and of the impact a congressional aide can muster.

As a CIA analyst, Sullivan insisted that his conclusions about Soviet duplicity be stated in an intelligence estimate, according to Adm. Stansfield Turner, who was CIA director from 1977 to 1981. Turner said that in 1978, after Sullivan lost the battle within the agency, he leaked a highly classified version of his thesis and supporting intelligence data to Richard N. Perle, then a key critic of SALT on the staff of Democratic Sen. Henry M. (Scoop) Jackson. When this was determined as a result of a polygraph test, Sullivan resigned from the CIA shortly before Turner would have fired him.

The same day he left the CIA, he moved to Capitol Hill as an aide to Sen. Lloyd Bentsen (D-Tex.). Sullivan became an active member of a network of conservative staff members that later became known as the Madison Group, after the hotel they made their meeting place. After a year, Sullivan and Bentsen parted by mutual consent, reportedly because Sullivan's views were too intense and one-sided for his boss. Sullivan then worked a year with Sen. Gordon J. Humphrey (R-N.H.), who reportedly fired him for failing to disclose his prior CIA connection with a controversy over an agent in the Soviet Union -- a matter Sullivan was looking into on Humphrey's behalf.

Sullivan's star seemed to be on the rise with the election of Ronald Reagan, who appeared to be as antagonistic to the Soviets and as scornful of SALT II as the Senate aide was. Sullivan was named to the Reagan transition team and, in this capacity, found himself on temporary duty as the second ranking official of the Arms Control and Disarmament Agency. In April 1981, however, he was abruptly ousted from that post when a more traditional conservative, Eugene V. Rostow, was named the ACDA's permanent director.

Now a foreign policy aide to four conservative GOP senators, Steve Symms and James A. McClure of Idaho and Jesse Helms and John P. East of North Carolina, Sullivan has finally seen the triumph of his views on SALT II. According to sources on all sides of the years-long battle, Sullivan played a role in building congressional and public pressure against SALT II and especially in raising charges of Soviet violations -- the issue on which Reagan based his May 27 announcement about abandoning SALT II restrictions.

Michael Krepon, director of the verification project of the Carnegie Endowment, who has followed the compliance debate closely, said Sullivan is "a true believer" in Soviet violations who played "an odd role" in bringing them to the top of the political agenda.

According to Sullivan, many in the administration initially considered Soviet violations "a secondary issue" in the overall SALT II debate, but came to accord them more importance and attention as controversy, and intelligence data, grew.

As a transitional official of the ACDA in early 1981, Sullivan compiled long lists of what he believed to be Soviet violations of SALT I and SALT II and urged that they be the basis for action. A study by career experts at the time disputed many of his charges, but the rebuttal document was highly classified and thus circulated to only a few in government.

After moving to Capitol Hill, Sullivan helped to generate a barrage of senatorial letters, speeches, press reports and legislative initiatives attacking SALT II in general, and Soviet noncompliance in particular. In Sullivan's first 18 months as a Senate aide, conservative senators fired off at least 23 letters to Reagan or other high officials of the administration demanding reports to Congress on Soviet violations. Sullivan drafted most if not all of these missives.

By mid-1983, the violations issue was appearing prominently in the press -- in part because of Sullivan's contacts with journalists -- and was increasingly prevalent in political discussion.

While there was (and still is) debate about many of the specific charges, there was growing consensus that the Soviets were exploiting ambiguities and operating at or over the edge of technical compliance with SALT II. As political and public opinion shifted to the right, there was less willingness than before to give the Soviets any benefit of doubt, and more inclination to accept the Sullivan view that the Soviets had set out to deceive and cheat all along.

In September 1983, shortly after the Soviets shot down Korean Air Lines Flight 007, the Senate voted 93 to 0 to demand an official report from the Reagan administration on Soviet noncompliance with SALT. The measure was sponsored by McClure, one of Sullivan's bosses, and the aide was active in getting it through. No senators wanted to be on record as opposing a report on violations, especially in an anti-Soviet climate, though the openly anti-SALT senators were probably in the minority.

Many in the administration had been reluctant to go public with charges that the Soviets were violating arms agreements because much of the evidence was both highly classified and ambiguous. Moreover, it was recognized that there could be great political impact on relations with the Soviets, on public backing for arms control and on continued U.S. adherence to SALT treaties.

The Senate vote and continuing pressures from senators associated with Sullivan forced the administration's hand. The Jan. 23, 1984, report to Congress on Soviet noncompliance committed the administration publicly to charges of Soviet violations and put the issue on the public agenda as it had not been before.

If there were violations of major consequence, as charged in the January 1984 report and two similar reports that followed, it stood to reason that the administration would have to do something about them. The subject was debated at length within the administration throughout much of 1985 and 1986 -- until Reagan's surprise announcement May 27 that he had decided to abandon the SALT II limits.

"I was pleased by it and, more important, my senators were pleased by it," Sullivan said of the SALT decision, which he heard about on his way home from leading a group of conservative Hill staffers on a trip to Central America. His battle against SALT has taken "a tremendous psychological toll and effort," Sullivan said.

A senior Reagan administration official who has followed the issue carefully, and who asked not to be quoted by name, called Sullivan "an unguided missile" who overstates the case in a way that loses credibility. He added, though, that Sullivan is a prime example of how potent a determined member of a congressional staff can be in shaping issues, even in such sensitive areas as U.S.-Soviet relations and nuclear arms control.

For now, Sullivan savors the victory over SALT -- even while continuing to worry that Reagan will somehow be persuaded to water down or reverse his decision.