By Emily Cadei, CQ Staff

After weeks of speculation and thousands of dollars in Republican attack ads against him, state Sen. Darrel Aubertine announced Thursday that he was not interested in running to succeed New York Rep. John M. McHugh .

“My priority must continue to be the work I have started in the state Senate,” said Aubertine, who was elected to the Senate in a special election in 2008, in a statement sent to the press. “I had a duty to finish out this year’s session.”

Aubertine was widely considered the Democrats’ top pick for the race, given his centrist record and ability to win a tough race in the traditionally Republican upstate region — he upset GOP Assemblyman Will Barclay in the 2008 race for the 48th Senate district.

Now they will have to turn to a field of approximately a dozen lower-profile candidates.

Because New York does not hold primaries for special elections, it is the party’s county chairs duty to pick the nominee for the yet-to-be-called race to replace McHugh, who President Obama has nominated to be secretary of the Army.

McHugh is waiting Senate confirmation but is not expected to face opposition. Once he is confirmed, Gov. David A. Paterson is expected to call a special election this fall, likely at the same time as the regularly scheduled 2009 November election.

The Republican party chairs tapped Assemblywoman Dede Scozzafava as their nominee on Wednesday.

The Democrat county chairs set Thursday evening as a deadline for prospective candidates to express their interest, forcing Aubertine’s declaration.

Leading the second tier are former Oswego mayor and former state Attorney General John T. Sullivan of Watertown; Daniel J. French, former U.S. attorney for New York’s northern district; Assemblywoman Addie J. Russell; and lawyer Michael P. Oot, who lost to McHugh by 30 percentage points in 2008.

The Democrats’ loss of Aubertine is Republicans’ gain, though given the razor-tight special election to replace Democrat Kirsten Gillibrand in the neighboring 20th District — won narrowly by Democrat Scott Murphy — it is still likely to be a heavily contested race.

And in the short term, the National Republican Campaign Committee is left to answer for the wasted cash it doled out on a series of robocalls, mailers and a television ad slamming the state senator this week.

Aubertine got in a knock at the GOP for what ultimately was a premature pre-emptive strike, commenting in his statement, “It’s no small wonder why the Washington Republicans are going extinct, and contributors should question why the money they’ve given was squandered here for no good reason at all.”