New York — New York could be Walter Mondale's big chance for a breakthrough against Gary Hart. Tomorrow's New York primary, which marks the halfway point in the Democratic campaign, has become central to Mr. Mondale's nomination strategy.
If Mondale is to lock up the nomination by the final primary in June, he must soon start building a wide delegate margin over Senator Hart. This means that New York, with its 285 delegates, is virtually a ''must win'' for the former vice-president.
Mondale is clinging to the lead here in pre-election polls, although some voter samplings indicate that Hart is moving up.
If Mondale can carry this state, his strategy then calls for all-out efforts in three other big-delegate races: Pennsylvania, Texas, and Ohio.
Together, those three states combined with New York send 855 delegates to the national convention in San Francisco in July - 43 percent of the number needed for the party's nomination.
Winning in all four states, and holding his own in other, smaller states, should put Mondale in a commanding position by the second week of May, his aides say.
Hart's staff, meanwhile, is cooking up a surprise of its own. Even if Hart loses in New York (polls show him six to thirteen points behind), the senator's staff says an upset in Hart's favor could be in the making a week later in next-door Pennsylvania.
Hart's own private polls show Mondale leading 44 percent to Hart's 43 percent in Pennsylvania. The state, Hart's aides say, definitely looks winnable.
Passing the halfway point in New York is forcing both the leading campaigns to look seriously at delegate totals.
Most of the states that have voted so far have been small potatoes in terms of delegates. New Hampshire, Maine, Iowa, and most other early states have little clout when the voting begins at the convention.
Beginning with Illinois last week and New York this week, however, the delegate-counters begin to look carefully at the totals. Just a few of these large states have enough votes to throw the nomination in one direction or another.
There are some disputes about how many delegates each candidate has so far. Hart, for example, is challenging the results of the voting in Puerto Rico. Both the Mondale and Hart campaigns, however, agree that Mondale is ahead. The official Mondale count is 742 to 419. The Hart count is 620 to 454, again with Mondale leading. A candidate needs 1,967 to be nominated.
Mondale strategists say they hope to be getting close to the magic number after the May 8 round of primaries in Ohio, Indiana, Maryland, and North Carolina.
Hart's strategists see little hope of catching Mondale in total delegates this month. Their plan is to gain strength steadily, then finish with a flourish in the final burst of primaries in June, including the year's biggest in California.
Even then, some planners on the Hart staff doubt that the senator will have a majority. At best, Hart may be forced to strike a bargain with uncommitted delegates to push his total over the top.
Political analysts say that for the first time in three decades, no Democrat may have wrapped up enough votes prior to the convention.
Dr. Austin Ranney, a political specialist with the American Enterprise Institute, uses a weather forecaster's phrase to describe the outlook. There is only ''a 30 percent chance'' that either Hart or Mondale will have a majority of the delegates after the final primary, he says.
That could set off a wild scramble by both sides to round up additional votes. In that setting, anyone with delegates to trade, especially Jesse Jackson , could play a pivotal role.
Hart's chief delegate counter, Michael Levy, says that the senator always knew he would be behind Mondale at this point in the race. The important thing is that since the first voting in Iowa, Hart has generally been gaining. In fact , the delegate totals are far more even at this point in the campaign than Hart himself expected them to be, Mr. Levy says.
As the primary campaign here goes into its final hours, neither side has been able to damage the other badly, despite some of the toughest words yet between the two front-runners.
Polls indicate that Hart has firmed his support here among independents and suburbanites, who form the backbone of his campaign.
But Mondale has kept Hart off balance, especially in New York City, by attacking Hart's positions on gun control and foreign policy.
On gun control, which Hart basically opposes, the senator may have lost some support in this crime-conscious city when he said: ''Frankly, the issue has never been in the forefront of my mind.''
On foreign policy, Mondale again questioned Hart's competence and sensitivity after the senator depicted European politics as less idealistic and more cynical than American politics. Hart called Richard M. Nixon the ''first European president we ever had, in the sense of kind of introducing a basic cynicism into public life.''