The Democratic primary for U.S. Senate is a preliminary in what is expected to be the most hotly contested bout on this year's congressional fight card.

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Alan Sandals and Chuck Pennacchio vigorously attack the temptation to look ahead to a fall matchup between incumbent Sen. Rick Santorum, R-Pa., and Bob Casey, the Democratic state treasurer. But that's what the national political community has been doing ever since Mr. Casey answered the call of national Democratic leaders by entering the Senate race.

Mr. Casey's appeal to the party hierarchy, in addition to the state record vote total he amassed in winning his current post, is that as a social conservative on issues such as abortion and gun control, he can moot wedge issues that have pushed socially conservative Democrats into the Republican column in recent elections.

Mr. Casey's Democratic rivals deride this logic, arguing that at a time when the Bush administration's poll numbers are slipping, the way to capitalize on the nation's political momentum is by nominating a candidate who embodies liberal Democratic principles.

The few public polls that have assessed this race suggest that the two long shots have had a tough time making that case, although both predict that Democratic voters will heed their messages as they attract more attention in the closing days of the race.

Mr. Sandals and Mr. Pennacchio are ideologically similar but offer contrasts in political style, and tactics. Both favor abortion rights while Mr. Casey opposes abortion. Both call for a rapid withdrawal of troops from Iraq while Mr. Casey, although a critic of the administration's conduct of the war, has resisted calls for a timetable for withdrawal. Both favor a dramatic shift toward a national health care system, while Mr. Casey has offered a more incremental approach toward expanding health care coverage.

Mr. Sandals, 52, is a Philadelphia lawyer specializing in pension issues. Mr. Pennacchio, 45, is a history professor from Bucks County. Mr. Pennacchio, a passionate stump speaker, has concentrated on building a grass-roots campaign to convey his message. Mr. Sandals, with a more analytical, lawyerly campaign persona, was the first candidate to air television ads in the hopes that a targeted commercial barrage in the last days of the campaign will attract just enough Democrats to make his long odds pay off.

Mr. Casey, 46, of Scranton, has remained relentless and focused on criticism of Mr. Santorum, who has no GOP opponent.