In a yes-you-can, no-I-can't shouting match, Sen. Paul S. Sarbanes (D-Md.) and Republican challenger Lawrence J. Hogan traded exaggeration and insult in the opening debate of their campaign over the involvement of the National Conservative Political Action Committee (NCPAC) in the Maryland Senate race.

Sarbanes, the man NCPAC hates, kept insisting that Hogan could get the independent lobbying organization out of the race if he wanted. Hogan, the man NCPAC loves, insisted he'd be happy to see NCPAC go, but said he can't do a thing to make that happen.

As it turns out, neither assessment was correct, according to the expert on such issues, the Federal Election Commission.

In their heated debate Tuesday night, Sarbanes asserted that Hogan, with a simple strategem, could get rid of NCPAC, the potent political group that mounted a $625,000 beat-Sarbanes campaign 18 months ago. Hogan could do the trick, Sarbanes said, by "communicating with them, breaking their so-called independence . . . . You haven't done that. You could do it very simply."

To that Hogan replied, "Paul, you don't understand the law . . . . The FEC prohibits any kind of communication between me and NCPAC and NCPAC and me."

So it went for several minutes in a WMAL-radio broadcast booth as Hogan's face turned red and Sarbanes' voice rose several decibels while the two men offered their interpretations of the complex federal election laws.

Though NCPAC takes credit for helping to defeat several prominent liberals in 1980, some of the candidates it seeks to help have been loath to identify with the group because of its negative tactics. In the Maryland race, Hogan has sometimes repudiated the group, even as its commercials continue to boost his candidacy. Meanwhile, Sarbanes has turned the role of man-under-attack into a political asset.

Under FEC rules, NCPAC may spend an unlimited amount of money in a campaign as along as it remains independent of all the candidates. That means no cooperation, consultation or suggestions going either way between NCPAC and the candidate whose cause it is championing, according to the FEC. If the group lost its independence it would be limited, as other political action committees are, to $5,000 donations in the primary and general elections.

Sarbanes asserted that if Hogan wrote to NCPAC, telling them his campaign plans, he'd break their independence. An FEC spokesman said yesterday that Sarbanes' idea would not necessarily have the effect he suggested. "It's a novel idea, but we've not really addressed it," said Sharon Snyder. She said the FEC would likely have to study the case and make a ruling, if it came up.

On the face of it, she said, the letter might compromise NCPAC's independence. But there would also be the question of NCPAC's constitutional right to make independent expenditures. "Can that be abridged by the mere issuance of a letter?" she asked. "The commission has never been asked that question before."

Hogan, dismissing Sarbanes' idea as "nonsense," maintained that such a letter would violate FEC laws. Because NCPAC already has spent far in excess of the $5,000 limit to aid his cause, he said he could be accused of accepting excessive contributions if he suddenly wrote to them.

The FEC spokesman said it would be difficult to accuse any candidate of accepting excessive contributions from a group if he wrote them a letter telling them to cease their activity.