In his four years in the United States Senate, Paul S. Sarbanes his maintained such a low profile that in a recent survey, even though half his constituents who were interviewed said they were favorably disposed to him, more than half of those could not say why.

These days, however, the low-key Maryland Democrat, who has made a career out of avoiding controversy, can't turn on a Baltimore radio station without hearing his name bounced back and forth across the airwaves like an electronic Ping-Pong ball, batted by ideological national groups from the right and left. And no one is more incredulous than the junior senator from Maryland.

"It's 19 months before the election," Sarbanes complains. "It's not fair."

The media tug-of-war that is pulling Sarbanes into the unaccustomed spotlight began last month when the National Conservative Political Action Committee (NCPAC) launched a $400,000 "get Sarbanes" campaign on Washington and Baltimore radio and television stations.

Last week, Democrats for the '80s, a political action committee put together by establishment Democrats after last November's disastrous showing by the party, joined the battle, buying commercials on five Washington and Baltimore radio stations to condemn NCPAC as "an extremist right-wing organization."

The Democratic response warns NCPAC director John T. (Terry) Dolan that "we're going to fight your lies and your distortions with a political tactic that you might find amazing. It's called the truth."

But as far as Sarbanes is concerned the modest $20,000 counter-campaign mounted by the friendly Democrats will do little more than raise his profile at a time when he would prefer to be quietly concentrating on whittling on some of the budget cuts proposed by the Reagan administration.

"Nobody asked me," says Sarbanes, furrowing his brow with concern over what he views as "an incredibly early start" on his still unannounced reelection campaign.

But because "you can't ignore these attacks," Sarbanes is gearing up for reelection about a year before he had planned, and, in the process, is finding himself portrayed to cost-conscious constituents as a big spender who opposes tax cuts for others while voting to raise his own salary.

Sarbanes believes he has been targeted by NCPAC in an effort to "intimidate" his 534 colleages in Congress. He decries the "lack of fair play" involved in an out-of-state (Virginia-based) third party organization pouring money into a negative campaign without regard to the consequences.

Meanwhile, the Maryland Republican Party has wieghed in with its own "get Sarbanes" campaign. GOP Chairman Allan C. Levey, in a fund-raising letter to party members, urged focusding on the 1982 Senate race, saying, "Our state has too long been represented by one of the most liberal senators in the entire U.S. Congress."

Levey's letter said Sarbanes voted for the "ultraliberal" SALT negotiator Paul Warnke, voted against the Kemp-Roth tax cut, supported President Carter on the "Panama Canal giveway" and "what really prompted this letter, voted against the confirmatin of Gen. Alexander Haig as President Reagan's Secretary of State."

Despite Sarbanes' disdain for long campaigns, he says he recognizes that "when you are under assault . . . you must address it. So sooner than otherwise, you are faced with the whole question of a reelection effort."

To Sarbanes, NCPAC's tactics "raise serious questions about how the political process operates."

Ordinarily, he says, two candidates and their political parties must "watch their words" because "they may come back to haunt them. That puts restraint on the political dialogue and encourages fair play and an approximation to the facts. But NCPAC is not accountable. They don't care how mad people get at them. After an election, they just vanish."

While his office has received about 1090 coupons clipped from NCPAC advertisements urging him to support President Reagan's economic program, Sarbanes says he has also received contributions of about $1,000 from more than 100 people who said they were offended by NCPAC's campaign.

Sarbanes says that in traveling around Maryland, he has found a strong reaction to the ads. "Intelligent voters won't be mainpulated by a high-priced advertising campaign from an out-of-state group. They sense the lack of fair play."

Dolan is confident this campaign -- like similar ones last year against incumbent Democratic Senators Frank Church, Birch Bayh and George McGovern -- will take its toll.

NCPAC is telephoning 100 Marylanders every third night, and preliminary results, according to Dolan, indicate that "Sarbanes is losing popularity. And for very specific reasons, such as opposing the president."

Peter Fenn, executive director of Democrats for the '80s, knows as well as anyone how effective Dolan can be. Fenn managed the unsuccessful reelection campaign of Sen. Frank Church (D-Idaho), who was one of NCPAC's targets last year.

Democrats for the '80s "wasn't formed to counter NCPAC," Fenn said. Its founders, who include chairman Pamela C. Harriman and her husband W. Averell Harriman, and party regulars such as Robert Strauss, Edmund Muskie and Stuart Eizenstat, have "a positive view." But according to Fenn, the attack on Sarbanes presented an irresistible opportunity for the organization to "tell people what NCPAC is and how it operates."

Dolan, for his part, calls the Democrats' ads "a publicity stunt meant to appeal to The Washington Post, not the people of Maryland."

It was a poll commissioned by NCPAC that revealed the vague views most Marylanders hold about Sarbanes. It also found Sarbanes leading a potential Republican opponent, Rep. Marjorie S. Holt, by 43.7 percent to 37.5 pecent, with 18.8 pecent undecided. It also said that of the 603 Marylanders interviewed, 42 percent identified themselves as moderates, 35 percent as conservatives and 19 percent as liberals.

Sarbanes scoffs that NCPAC's ads, which show a laborer criticizing him, have made "the hard hats . . . mad as hell, portraying them as dumb, uncouth types." A grin creeps across his face. "I think," he says, "it's going to come out all right."