Ronald Reagan appears to be picking up strength among moderate Republican voters and continues to dominate the field of those seeking that party's 1980 presidential nomination, according to a new Washington Post poll.

Long a favorite of conservatives, Reagan now appears to be doing just as well among rank-and-file Republicans who consider themselves moderate or even liberal in their political views.

Since the bitter Republican Party split in 1976, when the moderate wing of the party lined up solidly behind Gerald Ford and many moderates blamed Reagan for Ford's narrow loss, the key question in Reagan's quest for the nomination has been whether those wounds would ever heal.

Reagan has been widely perceived as attempting to move to the center this time around, putting less stress on conservative issues and seeking the support of leading moderates in the party. At this point, according to The Post's poll, that strategy seems to be working well.

Overall, Reagan is supported for the nomination by 41 percent of those who identified themselves as Republicans or independents leaning Republican in the poll. In a far distant second place is Sen. Howard Baker, with 20 percent. Third is Texan John Connally, with 15 percent, and fourth is George Bush with 5 percent.

About 20 percent said they are undecided as to which candidate they would support, so that among those interviewed who had made up their minds, Reagan actually is the choice of 49 percent.

In all, about 680 persons who identified themselves as Republicans or independents leaning Republican were among the 2,505 persons interviewed in The Post poll, which was conducted by telephone from Nov. 1 to Nov. 12.

Among the Republicans or Republican leaners who suppoted one candidate or another, half described themselves as moderates or as liberals and the other half as conservatives. Fifty percent of the moderates and liberals and 48 percent of the conservatives chose Reagan as their candidate.

One clear sign that the 1976 rift is healing, at least among the rank and file, was an expression of strong pro-Reagan sentiment among many who still would prefer Gerald Ford as the 1980 nominee. Among them, 44 percent list Reagan as their second choice -- and no other candidate comes close to that.

In addition, in hypothetical pairings against both President Carter and Sen. Edward Kennedy, Reagan keeps many more of those Ford supporters than do the other Republican contenders.

The Post poll reveals some other striking glimpses into the Reagan constituency. Republicans as a group are more affluent, older, better educated and generally more pro-business than the population as a whole.Much of Reagan's support, however, comes from what can be called the Republican "little guy" -- people who seem to stand apart from the overall stereotype.

For example, while he places first among Republicans in all income categories, the former California governor does best among those who report annual incomes in the $12,000 to $30,000 range, and poorest among those with incomes of more than $30,000. He does better among those with a high school education than those who are college educated, and as well with the youngest people interviewed as with the oldest.

In sharp contrast to other Republicans, Reagan does substantially better with rank-and-file Republicans who seem skeptical about big business.

Two questions in the Post poll dealt with people's attitudes toward business. One asked whether people agreed or disagreed with the statement that "the country would be better off if business were less regulated." Overall, among the 2,505 persons interviewed, 48 percent said they agreed, 30 percent disagreed and 22 percent said they had no opinion.

Among Republicans and independents leaning Republican, Reagan drew considerably more support from those who took the pro-regulation position in response to that question. Among those who agreed with the statement, 46 percent say they prefer Reagan as the 1980 nominee, but among those who disagree, 59 percent line up behind him.

The second question asked people whether they agreed or disagreed that "businessmen have too much power for the good of the country." Overall, 63 percent agreed and 26 percent disagreed, with 11 percent expressing no opinion. Among Republicans or independents leaning Republican who took the pro-business side on that question, 43 percent were Reagan backers. Among those who took the anti-business side, 53 percent said they supported Reagan for the nomination.

By contrast, while the numbers are small and not too much may be read into them for that reason, Connally, Baker and Bush were much more likely to draw their support from people who were pro-business.

Reagan runs weakest in the large cities but best in small towns, rural areas and suburbs of large cities. He leads his opponents in all regions, with enormous margins in the west and north central states. Among those who have made up their mind, he draws almost 50 percent support in the south, despite competition from southerners Connally and Baker, and from Bush, a northerner by origin who is considered a Texan by many.

The poll suggests that if Reagan has a shortcoming at this point, a feature his opponents can home in on, it may be his ultimate ability to be elected against a Democrat.

Having led Carter in several earlier polls, he now trails the president by 47 percent to 42 percent and by similar margins in several other recently reported national polls as well. He is behind Kennedy in The Post poll by 51 to 37.

The other Republican candidates, however, don't do nearly that well.