The congressional hearings on the Intermediate Nuclear Forces treaty had barely begun last month when Sen. Paul S. Sarbanes (D-Md.), one of the Senate's most liberal members, took on one of the treaty's foes, conservative Sen. Jesse Helms (R-N.C.).

Helms dangled classified documents and read from a letter from the CIA director in arguing that the INF agreement was impossible to monitor. But Sarbanes struck back, coolly calling his bluff by showing how Helms had distorted the contents of the letter.

It was a small victory for Sarbanes -- the sort of opportunity for national publicity that most politicians crave. But Maryland's senior senator did not capitalize on it; he made his point so blandly that Sen. Alan Cranston (D-Calif.) and other Foreign Relations Committee members moved in to hammer home the message -- and garner all the media coverage.

Sarbanes, 55, a serious-minded New Deal Democrat, has spent much of his career as a paradox in modern-day politics. And now, as he seeks his party's nomination to a third term in the March 8 Maryland primary, he seems to have no intention of changing his unorthodox ways.

Time and again he has been thrust to the center of major national dramas, including the House Watergate impeachment proceedings, the Panama Canal treaty debate and last year's Iran-contra hearings.

Yet Sarbanes generally has shunned Washington's limelight and political fast track in favor of an insider's role that has made him less visible than the other two leading Democrats in the state, freshman Sen. Barbara A. Mikulski and Gov. William Donald Schaefer.

Even on his home turf, the cautious, cerebral Sarbanes occasionally seems indifferent to public attention.

In October, Sarbanes arranged a breakfast meeting on the Eastern Shore with Rep. Roy P. Dyson (D-Md.), the mayor of Salisbury and other prominent area officials to lay groundwork for his 1988 reelection campaign. The event drew a strong turnout, but because of halfhearted advance work only one local reporter attended.

"He was making a tour of the Eastern Shore but he didn't tell anybody," said one baffled official. "If Barbara had been in there for a slab of toast, she would have had The Baltimore Sun, The New York Times and The Washington Post along."

"Paul is unique, but he's hard to get a handle on," said Rep. Benjamin L. Cardin (D-Md.), who holds Sarbanes and Mikulski's old 3rd District House seat in and around Baltimore. "He's extremely popular but goes around politics in a totally unconventional way. He's more of a framer of what we need to do . . . {than a champion of} a specific cause."

What Sarbanes sees as his virtues -- a highly judicious approach to issues, an aversion to self-promotion and an indifference to climbing the leadership ladder -- some see as flaws. Republicans contend that Sarbanes is a "political windsock" and Maryland's "invisible senator."

"Sarbanes has been very skillful at making a virtue of having no record at all," said Republican Noel C. Koch of Potomac, a former government counterterrorism expert who dropped out of the GOP primary race for Senate this year after concluding that Sarbanes was unbeatable in a general election.

C. Nelson Warfield, the executive director of the Maryland Republican Party, insisted, "If you ask the average man in the street what Paul Sarbanes has done for you, you'll have trouble getting an answer."

Sarbanes, who has no significant election opposition in either party, shrugs off the criticism, saying that the majority of voters understand and appreciate his style.

"I think the ordinary person, the ordinary sort of working person will say, 'He's for me, he's on my side, he's with me and fighting for me,' " said Sarbanes, who won reelection in 1982 with 63 percent of the vote. "I'm concerned about producing results, and I think that we've done that for the state and more broadly."

"The problem in this business is if you do pretty well, but run around yelling about it, the next time around you may not do so well because everybody's alerted to it," he said.

Thomas E. Mann, director of governmental studies at the Brookings Institution, said that Sarbanes' self- effacing style is refreshing and healthy, but he warned that it has a downside.

"Sometimes it looks like he's not engaged; he's indecisive at times, and so on," Mann said. "But I just take him to be a sort of quiet man. Those who know him well both respect and like him . . . . Months go by when I don't see him involved in things, and yet you never want to underestimate him."

Sarbanes is annoyed by media portrayals of him as a dispassionate politician. A recent Baltimore Sun series described him as a rational figure who rarely displays emotion or spontaneity -- a politician with the TV presence "of a well-dressed Mr. Rogers."

"I don't think that politics ought to be a sort of highly emotional charged context at all times, although on occasions it's important to have emotion," Sarbanes said. "But the democratic system depends in part on a reasoned discourse, a rational exchange.

"The most successful user of emotion in politics in the 20th century was probably Hitler, and look what he did," Sarbanes said. "That's not to reject the need for emotion in politics, but it's to point out some of the dangers of it."

As a youth, Sarbanes waited on tables at his father's restaurant in Salisbury, on Maryland's Eastern Shore. He became a top student and star basketball player, and his academic skills propelled him to Princeton, then to Oxford on a Rhodes scholarship and finally to Harvard Law School.

Karl A. Lamb, the academic dean at the Naval Academy who attended Oxford with Sarbanes, recalled that Sarbanes always demonstrated extreme self-confidence and a "judicial temperament" that militated against snap decisions.

"The first thing you sense about Paul is that he knows who he is," Lamb said. "There was never a question about him searching for an identity. A Gary Hart he isn't."

Sarbanes launched his political career in 1966, winning election to the Maryland House of Delegates. In 1970, he entered the Democratic primary for Congress in Baltimore and upset Rep. George Fallon, a 13-term incumbent. Six years later he ran successfully for the U.S. Senate in a tough field.

That such a low-profile politician is virtually assured reelection this year is explained in part by Maryland politics. With Democrats outnumbering Republicans by more than 2 to 1 statewide, Sarbanes is virtually invincible. Although he is probably more liberal than his state -- Sarbanes has the most liberal voting record of any member of the Senate, according to a Congressional Quarterly analysis of 1987 votes -- his ideology has given him broad-based support among traditional Maryland voters: organized labor, rank-and-file Democrats and the Jewish community.

Heavily Democratic Baltimore constitutes his power base, although he swept every county on the conservative Eastern Shore in 1982 and has a substantial following in Washington's affluent suburbs. Greek Americans have contributed heavily to his campaigns --

accounting for nearly one-third of all reported individual contributions to his reelection campaign this year. Sarbanes is of Greek descent.

"First and foremost, he is very much in tune, substantively and philosophically, with the Democratic Party and Maryland in general," said Keith Haller, a Maryland political consultant based in Montgomery County. "He has some core beliefs he projects extremely well."

Given the strength of his political base and his intelligence, some supporters expected that by now Sarbanes would have become presidential material, or at least the Senate's leading voice for traditional liberalism. What irks some of his admirers is his extraordinarily cautious, almost reluctant style, which they say has kept Sarbanes in back the of the pack on some important issues.

In 1979, for example, supporters of the Vietnam Veterans War Memorial, then a highly controversial proposal opposed by some veterans groups, asked Sarbanes to introduce legislation to donate federal land for the memorial site.

"He just didn't want to do it," recalled Jan Scruggs, the leader of the effort. "We just stopped getting our phone calls returned. Maybe he thought it would be controversial. He doesn't like a lot of controversy."

Republican Charles McC. Mathias, who was then Maryland's senior senator, subsequently agreed to introduce the bill. Sarbanes said last week that he does not recall the incident.

While many Senate liberals took an early stand against the nomination of Robert Bork to the Supreme Court, Sarbanes waited until a week before the Senate vote in October, when Bork's defeat was a foregone conclusion, to announce his opposition. Sarbanes said that "it seemed to me to make some sense" to await the conclusion of the Judiciary Committee hearings and a final committee report before taking a stand.

This year, Sarbanes initially signaled that he might stay neutral through the presidential primaries, even though his close friend and law school classmate, Massachussetts Gov. Michael Dukakis, was seeking the party's nomination. Schaefer and others predicted that Sarbanes would receive intense pressure from his supporters in the Greek community to back Dukakis. A week before the recent Iowa caucuses, Sarbanes dropped his neutral stance and flew to Des Moines to endorse Dukakis.

Last week, he said that he had not been pressured, noting that he had delayed making a decision until he completed his work on the Iran-Contra committee.

While Sarbanes is cautious, he is not conventional.

On Capitol Hill, where self-promotion is an art form, Sarbanes' office issues press releases infrequently and has not sent out a constituent newsletter -- a popular campaign device -- since 1985, when Sarbanes returned from a meeting in Moscow with Soviet leader Mikhail Gorbachev.

"He really doesn't like the art of self-promotion," said Christine Sarbanes, the senator's British-born wife. "I think he's always felt that you shouldn't have to promote yourself -- that if you're doing the job right others will perceive it."

Sarbanes rarely introduces legislation, arguing that most bills never see the light of day and that he is better off trying to amend others' legislation. During his second term, Sarbanes has introduced 17 bills, and only one of those -- a measure renaming the Baltimore-Washington Parkway after former representative Gladys Noon Spellman -- was approved.

At the same time, he sponsored eight amendments that were approved, including a neighborhood reinvestment measure, a rider to the 1986 antiapartheid act suspending air service between the United States and South Africa, and an amendment requiring a noise abatement study at Baltimore-Washington International Airport.

While critics wonder what Sarbanes has accomplished, his peers in the Senate generally admire him and view him as effective.

Sarbanes, the third-ranking Democrat on the Foreign Relations Committee, also serves on the Banking, Housing and Urban Affairs Committee and is chairman of the Joint Economic Committee.

His influence stems in part from a close relationship with Senate Majority Leader Robert C. Byrd (D-W.Va.), who often seeks Sarbanes' advice. As a participant in the Democrats' legislative review committee, Sarbanes has helped to shape policy on Social Security, tax reform, aid to the Nicaraguan rebels and campaign finance, according to Byrd.

"He's a thinker, a clear and thorough thinker," Byrd said recently. "He has a cool judgment in which I put a great deal of trust."

Sarbanes and other banking committee members successfully fought Reagan cuts in the Urban Development Action Grant and Community Development Block Grant programs. He claims credit for preserving an innovative "Nehemiah" home equity loan program for low-income families included in the new housing law. Also, he helped draft sections of the Senate omnibus trade bill dealing with export controls and international monetary policy.

On local issues, Sarbanes has quietly tended to his state's needs, working with other Maryland politicians to obtain funding to dredge the Baltimore Harbor, clean up the Chesapeake Bay -- although here again he was overshadowed by Mathias -- restore beaches at Ocean City and complete the Washington area Metro subway system.

He surprised some when he took the Senate floor in late 1986 to wage a disruptive nine-day filibuster to try to defeat a bill creating a regional airports commission to lease the federally owned and Dulles International and National airports.

Sarbanes had collected enough political IOUs as a loyal Democrat to earn the indulgence of his colleagues, who did not complain about the filibustering.

The filibuster still failed, but it gave Maryland transportation officials and Rep. Steny Hoyer (D-Md.) the leverage they needed to negotiate a deal with the U.S. Department of Transportation to pump $75 million in federal funds into runway expansion and other improvements at BWI.

Sarbanes first gained national attention in 1974 as a member of the House Judiciary Committee investigating the Watergate scandal. His impartial style drew kudos, and he was asked to draft the first article of impeachment against President Nixon.

As a freshman senator, Sarbanes was slow to embrace the controversial Panama Canal treaty, but he ultimately helped manage the 1978 floor fight against conservatives that led to its ratification. He weathered a nasty, high-priced attack from the National Conservative Political Action Committee (NCPAC) to win reelection handily in 1982. Last year, he served on the Senate select committee investigating the Iran-contra affair.

"In a way, he's never had to go out looking for causes," Christine Sarbanes said. "They've always come to him."