In winning six of the first seven 1980 presidential primaries, Ronald Reagan has demonstrated convincingly the depth of his support among conservatives, older people and regular Republicans. He has yet to convince skeptics, however, that he can attract the backing of moderates, younger voters, independents and Democrats.

Reagan, harking back to his two gubernatorial victories in California, says he has demonstrated that he can win Democratic votes. Potential opponent Gerald R. Ford argues that Reagan has shown since then that he is too conservative to be elected president.

While a highly selective case can be made for either proposition, the evidence at this point remains inconclusive.

Reagan backers can take comfort from the fact that their candidate is running ahead of his 1976 primary performances. Reagan opponents can cite, as four did today, a recent poll showing President Carter defeating Reagan but losing to Ford.

Reagan has done better than he did four years ago in winning primaries in New Hampshire, Vermont, Florida and Georgia. His percentage slipped slightly in Massachusetts. Alabama and South Carolina, which Reagan won by big margins this time, did not hold primaries in 1976.

No such comparisons can be precise. On the other hand, Reagan was running against an incumbent president in 1976, and might reasonably be expected to do better this time; on the other, he has been competing against a large field, which tends to make any candidate's percentage lower.

The most impressive comparison for Reagan is in Florida, where, as a challenger, he won 47.2 percent of the vote against then-president Ford's 52.8 percent in 1976. This time Reagan won 57 percent to 30 percent for George Bush.

Speaking of the Florida Republican primary, the Almanac of American Politics 1980 points out, "This is an election in which Florida truly becomes a non-southern state. Most of the state's registered Republicans are transplanted Yankees. . . . Accordingly, Gerald Ford's [1976] victory over Ronald Reagan was hardly a surprise; it mirrored his support in the suburbs of Chicago, Detroit, Philadelphia and New York."

Pinellas County, which includes St. Petersburg, is considered the most moderate and non-southern of all Florida counties. It was here that Ford scored his biggest margin over Reagan in 1976, beating him 60 percent to 40 percent. On Tuesday, with a lower turnout than four years ago, Reagan won 50 percent of the vote compared with 29 percent for Bush.

The Reagan comparisons in other states:

In New Hampshire, where Reagan started his bandwagon, he won 50 percent of the vote against a six-man field containing three active candidates. Ford won 49.4 percent in 1976 to 48 percent for Reagan.

The most impressive aspect of Reagan's New Hampshire victory was the loyalty of the candidate's supporters.Four-fifths of those who voted for Reagan in 1976 did so again in 1980. Reagan was particularly strong among older voters, conservatives, working-class Republicans, French-Canadians, southern European ethnic groups and Roman Catholics.

In Vermont, Ford in 1976 won 84 percent of the vote and Reagan 15 percent. This time Reagan had 31 percent, compared with 30 percent for second-place John B. Anderson.

In Massachusetts, Reagan was badly beaten in 1976 by Ford, who had 61 percent of the vote to Reagan's 33 percent. This time Reagan had 29 percent, compared with 31 percent each for Bush and Anderson.

In Georgia, Reagan defeated Ford 68.3 to 31.7 percent in 1976. Reagan won 73 percent of the vote this time.

The only primary Reagan has won so far in which Democrats and independent were free to participate was in South Carolina, where Reagan defeated John B. Connally by nearly a 2-to-1 ratio and knocked the former Texas governor out of the race.

But South Carolina, while nominally Democratic, is behaviorally Republican in most national elections. South Carolina was one of six states to go for Barry M. Goldwater in 1964, and it remained faithfully Republican in presidential elections until turning to fellow southerner Jimmy Carter in 1976.

National polls suggest that Reagan's general election appeal is limited, at least against Carter. ABC News-Harris Survey this week showed Ford running ahead of Carter by 54 to 44 percent in a nationwide sample of 1,498 likely voters. Reagan trailed Carter 58 to 0 in the same sample.

Some in the Reagan camp point to the extreme fluidity of the Harris findings. Only a month ago, Carter led Reagan 64 to 32 percent, indicating that the president's margin may be slipping.

Reagan's oft-repeated statement that he has demonstrated bipartisan support by winning California by a million votes in 1966 and "by almost that many four years later" is as suspect as any poll. Reagan's margin slipped to just under 500,000 in 1970, with most of the loss coming in Democratic areas.

Since 1974, Reagan has been identified as a national conservative rather than as a fairly moderate governor, and this perception of him probably was deepened by his 1976 challenge to Ford.

When Reagan started to win primaries in 1976 on the strength of his opposition to the Panama Canal treaties, national polls showed him dropping among all other voters at the same time he was making gains among Republicans.

Washington Post poll taken last November indicated that Reagan was broadening his appeal to Republican moderates, many of whom listed him as a second choice to Ford. A Ford candidacy, therefore, may tend to push Reagan back to a conservative base, which might help him in the southern and western primaries, but would almost surely limit his appeal in the 1980 general election.