Philadelphia — On the eve of the crucial Pennsylvania primary an uneasy anticipation is felt in the camps of all four presidential candidates competing here. Each thinks its man has a chance to win.
Victory in the popular-vote contest in both parties could be a matter of a few points either way, the candidate spokesmen say. On the other hand, large numbers of undecided voters -- with some estimates running as high as 30 percent -- could produce a one-sided outcome at the last minute, making the Keystone State's primary too volatile for the campaign pros to call.
"It's close, I tell you it's close," says John Rendon, former political director for the Democratic National Committee, now working for President Carter in Pennsylvania.
In the convention delegate chase, Mr. Carter and Ronald Reagan are expected to add heftily to their impressive leads, even if they lose the popular vote by possibly narrow margins.
Cutting into the comfort of the front-runners' delegate advantage is the worry that a Pennsylvania loss might expose a basic softness in their candidacies that could hurt them after the convention. With seven months before the election, recent polls are showing half the voting public already would prefer something other than a Reagan-Carter choice in November.
Clearly their Pennsylvania rivals, George Bush and Edward M. Kennedy, hope a win for them here would make the Carter and Reagan leads appear less invincible.
Mr. Bush's candidacy is the one most on the line in Pennsylvania.
"Coming back from this far behind has never been proven possible in national politics," concedes Bush campaign director James Baker.
If Mr. Bush fails to stun Mr. Reagan in the Pennsylvania popular vote, it is hard to see another state where it could be done, Mr. Baker says.
"If we do well in Pennsylvania -- if it's perceived as an unexpected victory for us -- it would restore a degree of momentum to our campaign," Mr. Baker says.
Pennsylvania Republicans will vote separately for convention delegates and in a nonbinding "beauty contest" popular vote. "They'll win more delegates than we will," Mr. Baker says. "But we want to prove to Republicans we can beat Reagan one-on-one outside the South. There are a lot of moderate Republicans looking for an alternative to Reagan."
Mr. Reagan's delegate stalkers are confident they will take at least 50 of the state's 83 GOP convention delegates. "But the popular vote's too close to call -- five points one way or the other," says Rick Robb, a Reagan strategist here.
"They've shot the works here," Mr. Robb says of the all-out Bush campaign in Pennsylvania since early April. "We'll wind up spending $135,000 max. We'll be outspent 10 to 1. But Mr. Reagan's position now is not unlike Carter's in '76 -- the numbers in Reagan's delegate lead are grinding."
Should Mr. Reagan falter despite his commanding lead with almost three-fifths the delegates decided, Gerald Ford is still given a better chance than Mr. Bush if the nomination is made into an open convention choice, political analysts say.
On the Democratic side, many of Senator Kennedy's people anticipate a Pennsylvania win, despite late polls showing him trailing. "We're doing well in Philadelphia," says Carol Cesey, national delegate strategist for Mr. Kennedy. "It's western Pennsylvania where our support hasn't been in line."
Unlike the New York primary, where the Kennedy win took most observers by surprise, there has been no issue like the President's UN reversal on Israeli settlement policy to galvanize anti-Carter sentiment here, Carter backers here say.
"The critical issue is national security," Carter- Mondale spokesman Chris Matthews says. "Iran is the current symbol of the challenge to our national security. Afghanistan isn't seen as directly threatening to Americans as is Iran. If Carter is perceived as stronger in dealing with such threats, then we'll win on Tuesday."