On the surface, Gary Hart's campaign in Pennsylvania looks impressive: * Nine thousand volunteers are working across the Keystone State, knocking on doors and making telephone calls.
* Campaign offices have been opened in every congressional district. There are three Hart offices in Philadelphia alone.
* Two Colorado busloads of Hart volunteers, known as ''Gary's Guerrillas,'' are racing about the state to boost his campaign.
* Polls show Senator Hart at least as strong as Walter Mondale in Pennsylvania, or even a little bit ahead.
Despite all of this, Hart must be considered the underdog when Pennsylvanians vote next Tuesday.
If this were another state - California, for example - the outlook might be different for Hart. But Pennsylvania shapes up as one of the toughest possible places for the senator to quickly rekindle his campaign after his worst-ever loss in New York. This is a state almost tailor-made for Mr. Mondale.
Just look at the playing field:
Pennsylvania is a labor stronghold. More than 40 percent of the voters next week are expected to be from union homes. It's interesting to note that in New York, Hart ran as strongly with nonunion voters as Mondale. It was the union voters who provided Mondale with all of his margin of victory.
il3l,4p Another factor: Unemployment is high here. In past primaries, a high jobless rate has worked in Mondale's favor. Polls show that voters believe one of Mondale's greatest strengths is that he ''cares about people'' and will do something about unemployment.
Democratic voters here also consider themselves more conservative than in some other states. That should help Mondale, since his greatest strength has been among moderate and conservative voters in recent weeks. In Connecticut and New Hampshire, where the largest number of voters call themselves liberal, Hart ran away with the election.
The average voter in Pennsylvania is a little older than in many other states. Older voters, it seems, pick Mondale over Hart by as much as 2 to 1.
There is a lot of poverty in Pennsylvania, and a very large pool of low-income voters. That's another Mondale advantage.
Finally, more than half of Pennsylvania's Democatic voters are Roman Catholic. This week in New York, Mondale scored a solid victory among Catholic voters. Interestingly, among Protestants, Hart defeated Mondale 27 to 26, according to ABC News exit polls.
As if all of this were not enough, there is one other mammoth problem facing Hart and his supporters here.
Back in the days when few people knew who Hart was, and when he had little money or staff, the deadline passed for filing delegate slates for the primary here. Out of 117 spots for delegates on the ballot, Hart was able to put up only 47 names.
When voters go into the polls next Tuesday, they are supposed to first vote in the ''beauty contest'' part of the election - Hart vs. Mondale vs. Jesse Jackson. But then they are supposed to vote for several delegates to represent their candidate at the convention.
In each district, Mondale has the proper number of names, with the delegates clearly identified as Mondale representatives. Hart has delegates in less than half the districts.
To overcome this problem, Hart's staff has recruited delegates who were previously pledged to other candidates who have since dropped out. Most of them are former Alan Cranston delegates or former John Glenn delegates.
The trouble is, there's no way for voters to look at the ballots and tell which Glenn delegates and which Cranston delegates have promised to vote for Hart.
To deal with this problem, Hart workers are passing out 2 million slate cards to identify the delegates in each district who have promised to back Hart.
They are also running ads in newspapers listing the names of former Cranston and Glenn delegates now pledged to Hart. Voters are being encouraged to clip out the lists and carry them into the polling booths. But there is no guarantee that all this effort will succeed. A similar effort in Illinois was a flop.
''It's a real problem for us, I won't deny it,'' says Elizabeth Cain, an aide in Hart's state headquarters here. ''A massive educational effort is necessary. All our phone banks are busy explaining the procedure to voters,'' she says.
The Third Congressional District in Philadelphia illustrates how tough it will be. Voters are supposed to pick seven delegates there for the national convention. Hart has none under his name, but he has recruited seven from other candidates to help him. One had been for George McGovern. Two formerly backed Senator Cranston. Four were for Senator Glenn.
Even with intense voter education, most Hart supporters are expected just to ignore that part of the ballot. This raises the possibility that Hart could win the popular vote here, but see most of the delegates wind up in Mondale's pocket.
Just about all the polling here shows the race very, very close. One of the most recent, conducted in late March by the Gallup Organization, gave Hart a narrow 42-to-40 lead, with Jesse Jackson at 8 percent and 10 percent undecided. Among ''likely'' voters, the race was even tighter - 42 to 42, with 9 for Jackson.
A Gallup official notes that other questions on the poll indicated that Mondale's support was firmer than Hart's. This means, he said, that Mondale backers are more likely to vote next Tuesday, and that Hart supporters are more likely to switch to Mondale during the volatile 72 hours just before the polls open.