House Majority Leader Thomas W. Moss Jr., a Norfolk Democrat who's used to having things his way, last fall found himself campaigning hard for his first reelection in a single-member district. Never before had he had to go out on his own, without the help of a citywide slate of Democrats. Never before had he faced a determined opponent like Edythe C. Harrison.

Harrison, a delegate and erstwhile colleague of Moss', was merciless. She zeroed in on Moss' failure to support the Equal Rights Amendment, charged him with numerous conflicts of interest and accused him of working to defeat a bill that would have banned state meetings in clubs that discriminate by race, creed, color or sex.

Moss won, but only by 580 votes.

This year, there are signs that the majority leader, up for election again this year, is changing his stripes. The man targeted last year by women's groups statewide has suddenly, out of the blue, come out for the ERA--a gesture that some note is largely irrelevant because the issue is years away from any reincarnation in Virginia.

Moss, a lawyer, also is saying he won't take any more clients before the state Alcoholic Beverage Control Commission, this in response to charges by Harrison and others that he had abused his influence over the commission.

This year, he is a cosponsor of the session's most visible ethics reform measure. Not only has he signed onto Fairfax Sen. Adelard L. Brault's bill, but he defended it before a Senate committee and plans to carry it onto the House floor.

Finally, Moss, stung by the charge that he had helped kill the bill against discriminatory clubs, called up Del. Bernard S. Cohen (D-Alexandria) before the session to ask if he could put his name on any similar bills Cohen might introduce this year. Such a bill, with Moss' name on it, already has cleared a critical hurdle in the House.

Does all this suggest a new Tom Moss? Has life in a single-member district chastened the once-arrogant majority leader, making him more sensitive to the concerns of his constituency?

Emphatically not, Moss says. With the exception of ERA, on which he concedes he had been "passive-negative," Moss argues that all he has done this year is clear up distortions he says Harrison threw at him during the campaign.

"What I am trying to do is make sure that my positions cannot be distorted again," he said. "But those positions have not changed."

"This was the first time I had such vociferous opposition and the kinds of things said about me taught me the importance of making my record clear," he said.

On the ERA, he takes great trouble not to give any credit to the women's groups that targeted him last year, saying instead he changed his position out of deference to supporters, among them teachers, whose Virginia Education Association was barred by its members from contributing to him last year because of his non-position on ERA.

Yet Moss can't deny that the fallout from the campaign has had its effect. For instance, he acknowledges that his decision to taper off his practice before the ABC was in response to public perceptions.

"From the standpoint of public opinion, it was an issue, and if that's the way it's going to be, and since it was so little of my practice, who needs it?" he said.

Some observers draw a more direct correlation between Harrison's attacks and Moss' new-found support for the ERA.

"I would say that little experience had something to do with it," said Del. Robert E. Washington (D-Norfolk). But, said Del. William P. Robinson Jr. (D-Norfolk), the change in Moss "is more a matter of style than anything else. On the guts issues, he's unchanged."

Moss and the other members of his delegation were never in favor of single-member districts, adopted statewide in Virginia only at the insistence of the Justice Department. Moss, for one, said it was the nature of his opposition, not of his district, that made last year's campaign different.

Others disagree, noting that in multimember districts, individual candidates tend to lost their identity to the slate as a whole. They note that only in a head-to-head race could Harrison have turned Moss' record into the sole issue of the campaign. Without a single-member district, they say, Moss would not have been compelled out of political self-interest to speak out clearly on ethics, ERA and other issues.

"None of this happens in a vacuum," said Marianne Fowler of Alexandria, chairman of the Virginia Women's Political Caucus and a frequent target of Moss' ire. "As cumbersome as it might be, the political system is at work."