A new Quinnipiac University poll found Republican challenger Pat Toomey with a narrow lead over Sen. Arlen Specter.

Statistically, the survey's trial race -- 43 percent for Mr. Toomey and 42 percent for the incumbent -- was essentially identical to the school's last survey in July, when Mr. Specter was ahead by the similarly tiny margin of 45 percent to 44 percent. Both results were well within the survey's 3 percentage point margin of error. But the reversal of their positions threw a symbolic spotlight on the veteran's vulnerability in the closely watched race.

When he made his surprising departure from the Republican Party earlier this year, Mr. Specter said he didn't want his political fate to be decided by a jury of the GOP electorate. The new findings suggest that a general election jury might also render a thumbs-down verdict on his re-election.

The survey did show Mr. Specter retaining a lead over Rep. Joe Sestak in the Democratic primary, but his margin for renomination, while still significant, had narrowed since Quinnipiac's July assessment. The incumbent led his Democratic challenger 44 percent to 25 percent in a primary matchup, down from 55 percent to 23 percent in the earlier poll.

Mr. Toomey and Mr. Sestak were nearly even in their general election test, with the Democrat trailing, 38 percent to 35 percent.

Among all voters, Mr. Specter's unfavorable rating has soared since his party switch. Forty-six percent of those surveyed said they had an unfavorable view of him while 42 percent held a favorable view. A year ago his favorable rating was 55 percent and unfavorable only 23 percent.

The sagging numbers come as the Obama administration continues to demonstrate its determination to shore up Mr. Specter's candidacy. President Barack Obama headlined a fundraiser for the senator last month in Philadelphia. Vice President Joe Biden campaigned with him over the Labor Day weekend and will return to Pittsburgh to appear with him at the Allegheny County Democratic Party's Kennedy Lawrence dinner later this month.

But, for now at least, that administration backing appears a somewhat devalued political asset. Mr. Obama's job approval rating in the state was 49 percent less than a year after he captured the state's electoral votes by the largest margin of any Democrat in half a century. In February, the president's approval rating in a similar Pennsylvania survey was 63 percent.

Most Pennsylvanians said Mr. Obama's support for the incumbent made no difference in their Senate choice, but for those to whom it did matter, it was a net negative. Sixty-eight percent said the president's endorsement made no difference in their Senate choice; 12 percent said it made them more likely to back Mr. Specter while 18 percent said less likely. The findings for independents were close to the overall sample while Republicans and Democrats differed on expected partisan lines.

While his numbers have been battered among Republicans and independents, Mr. Specter has retained most of his support among the voters of his new party.

Fifty-two percent of all voters said Mr. Specter does not deserve to be re-elected, among them 81 percent of the Republican and 53 percent of independent voters. But 60 percent of Democrats said he did deserve another term, with 25 percent disagreeing.

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