WASHINGTON -- Former House Speaker Newt Gingrich is coming to the aid of Rep. Sherwood Boehlert, criticizing his primary opponent and warning a conservative group that he will become "personally involved" in the race if they don't back off.

Gingrich's defense of Boehlert, R-New Hartford, came in a chiding letter to the president of Club for Growth, an activist group that supports candidates who are fiscal conservatives.

A copy of the letter was obtained by the Associated Press.

The group, led by Stephen Moore, was active in the ultimately unsuccessful effort to unseat Pennsylvania Sen. Arlen Specter in a primary contest that was viewed as a test of the Republican party's right wing, and is considering a similar attempt against Boehlert.

Gingrich, the architect of the "Contract with America" that helped Republicans take control of the House in 1994, argued in the May 28 letter that Boehlert has a strong record as a fiscal conservative.

He also contends Boehlert's primary challenger, Auburn surgeon David Walrath, does not have similar budgetary bona fides.

Moore, whose group has not decided whether to become actively involved in the campaign, sounded unfazed by the criticism from Gingrich, an icon in many conservative political circles.

"I'm writing Newt back a letter right now saying we really respect his opinion because he's one of our heroes, but we think this is a clear choice between a conservative Republican in Walrath and a liberal Republican," Moore said.

Club for Growth will likely decide in about three weeks whether to become involved in the Boehlert-Walrath primary, Moore said.

Walrath campaign manager Brett Mecum said the campaign was seeking an apology from Gingrich for advancing what he described as "a complete spin and fabrication of what the truth is."

"Sherry Boehlert's office can plainly see that the minute the Club for Growth gets involved in this race, he loses, plain and simple," said Mecum.

In his letter, Gingrich also issued a warning to Club For Growth: "I am prepared to become personally involved in helping Sherry defeat Walrath and in so doing, I believe that it will become obvious that Club for Growth is not a serious organization when it comes to helping pro-growth candidates reach elected public office."

Gingrich was traveling abroad and could not be reached for comment.

Repeating a point often made by Boehlert supporters in the contentious primary campaign, Gingrich's missive charged Walrath, as a county legislator, voted for an increase in county property taxes.

"Hypocrisy is not one of the characteristics I'd look for in a tax reformer," Gingrich wrote. "Not only is Walrath wrong on fiscally conservative policy issues, he also is not a strong candidate."

Walrath's campaign manager said the charge was untrue, and argued the letter may ultimately help Walrath win official backing from the Club for Growth.

Boehlert spokeswoman Melissa Carlson said Gingrich has volunteered to help the re-election effort, and that the two men have been friends for years.

"He has offered to come up (to the district) and assist the congressman in any way he can," said Carlson.