Democrats take on bitter tone of Ford-Reagan in '76.

As New Yorkers vote today, a leading political scientist observes that the Hart-Mondale clash has begun to resemble the bitter 1976 Reagan-Ford race that spilled right onto the convention floor.

Dr. Austin Ranney, a scholar at the American Enterprise Institute, says the seesaw Democratic struggle could remain unsettled even after the final primary in June.

The close contest also raises a slim possibility that Democrats could eventually turn to a third, compromise candidate in an effort to pull the party together, says Dr. Ranney, who is a former president of the American Political Science Association.

The focus of the Democratic race today will be on New York and Wisconsin, where voters will choose among Walter Mondale, Gary Hart, and a surprisingly strong Jesse Jackson. The New York election will select convention delegates; but in Wisconsin, the voting will be a nonbinding ''beauty contest.'' Delegates there will be chosen later at party caucuses.

Dr. Ranney says that in primaries so far, Mr. Mondale has clearly played the role of incumbent, as Gerald Ford had to do in 1976. Mr. Hart, like Ronald Reagan in '76, ''is coming up on the outside. He's challenging. He's the attacker and Mondale is the defender.''

This pattern gives Hart a significant political advantage, Ranney says, even though Mondale has recently mounted counterattacks against Hart's voting record in the Senate.

Ranney, who recently wrote on the subject of politics and television in his latest book, ''Channels of Power,'' also made these points:

* The role of TV in the Democratic campaign has been critical. ''For the great mass of the people, political reality is what they see on television.''

* Hart's foreign policy positions are emerging as a kind of ''updated McGovernism.'' This could help him in the primaries, but hurt the party in the general election.

* Neither Hart nor Mondale is entirely representative of what was once the mainstream of the Democratic Party. That mainstream, which was led by senators like Hubert H. Humphrey and Henry M. Jackson, supported policies that were simultaneously strong on both civil rights and national defense.

* Jesse Jackson will be a major factor for a long time in the party if he continues to pick up strength.

Here are excerpts from the the Ranney interview:

Hart still isn't very well known to voters. He calls himself an independent, Jeffersonian, Western democrat. How would you characterize his positions?

On foreign issues, he comes down very much as a McGovernite liberal. He says, ''Let's not get involved in foreign affairs; let's not support corrupt, right-wing dictatorships; let's only support pure democracies.'' It certainly has one of its roots in isolationism. ''No more Vietnams'' is a kind of isolationist policy.

The Hart-Mondale fight is getting rather bitter. What will the effect be on the Democratic Party?

I would say that right now, and maybe ever since the early 1970s, the Democratic Party is to a political party what the United Nations is to a government. It has a lot of the trappings and appearance, but it really is a collection of a lot of independent, sovereign powers. They negotiate with each other, but they don't feel any strong loyalty to each other.

In a wide-open nominating process like this . . . you've got to distance yourself from the other guy. In some sense, the closer together they are ideologically, which is very much the case here, the more you have to get a little nasty to give people good reason for voting for me instead of that other guy.

Does Hart or Mondale have a strategic advantage in this race?

Hart is coming up on the outside. He's challenging. He's the attacker and Mondale is the defender. It's always better to be on the attack than on the defense. Second, in Mondale's case, this is it. It's now or never for him. Hart can tell himself, quite legitimately, that he's going to come awfully close this year. But if he doesn't make it, he's got a huge head start toward 1988, possibly a vice-presidential spot, and he might even make it this year.

Does either of these candidates appeal strongly to Henry M. Jackson-Hubert H.Humphrey Democrats, who used to be the mainstream of the party?

I guess in many respects they would feel somewhat closer to Mondale than Hart. Mondale, after all, was the protege of Humphrey. Mondale made a real effort. He appeared before the Coalition for a Democratic Majority (an organization of Jackson-Humphrey Democrats). He is very closely associated with organized labor. And he is seeking to win the nomination by pasting together the parts of the party.

Hart is running very much as Jimmy Carter did, as George McGovern did. He's running as an outsider, the man with the new ideas, the new approach, with, I think, relatively little concern for the Democratic Party and its history and tradition.

Where will Jesse Jackson be after this campaign?

I don't think there's any question that Jackson is going to be a major factor in Democratic Party politics for some time to come, beginning with the convention this year. He is going to wage a very stiff fight on the rules - the double primaries, for example. He's going to put people on the spot, particularly Mondale, but to some degree Hart as well. He's going to be very visible. If he loyally supports the ticket, and there's a big black vote, then he will come out in November as the unchallenged leader of American black politicians and one of the real powers in the Democratic Party.

Have there been any big surprises this year?

In some sense, the surprise this year is that Mondale was able to come back. Very much the same thing (defeat of the front-runner) happened to (Edmund) Muskie in '72 and (Henry) Jackson in '76. One had every reason in historical precedent to think that Mondale was dead after New Hampshire. But he's holding his own.

What role is TV playing in this campaign?

By focusing on the horse race (let me say, I don't blame them for doing that) , television has performed as it has in past years. Like past years, it focuses on front-runners and challengers and so on. In Iowa it declared not only a winner but a second-place finisher. In this way, TV has played a very important role in the Hart candidacy, and will continue.

I also think television's performing pretty characteristically. The person who is behind gets more sympathetic treatment than the front-runner.

After New Hampshire, it was courageous Fritz (Mondale) with the world crumbling around him, just as before New Hampshire it was dull Mondale having it all locked up, and the fresh voice out of the West challenging him.