The affair opened in February, when Sen. Arlen Specter (R-Pa.) quietly slipped a small provision into a massive spending bill that effectively altered the rules on mass mailings. And it reached a culmination of sorts on a recent Monday morning in Allentown, Pa., the backyard of Specter’s chief political rival, Rep. Pat Toomey (R).

It was there that Specter appeared for a town meeting with constituents. While generic in most respects, this particular event had been organized with the help of the Senator’s very own “pilot program.”

The program originated in the fiscal 2003 omnibus spending bill. The provision authored by Specter, a senior member of the Appropriations Committee, enables Senators to dip into a $500,000 fund to pay postage on postcard-type notices for town meetings just like the one in Allentown.

And it was on June 4 that cards began hitting mailboxes across the Eastern Pennsylvania city.

“As your United States Senator, my number one priority is keeping abreast of your needs and concerns, so please try to attend. Together we can achieve a great deal for Pennsylvania,” read the notice, signed by Specter.

Under the Senate’s somewhat labyrinthine ethics rules, all mass mailings must be sent under the frank. But there is also a subset of guidelines for certain mail pieces — such as town meeting notices — for which a Senate office must use its official funds, not its franking allowance.

So, in setting up the $500,000 fund, Specter essentially created a subsidy for Senators wishing to notify constituents when they will be in the neighborhood. The program would pay half the cost of such mailings, thus taking a smaller bite out of Senate office budgets.

“It always seemed to me that if you were willing to go to a town meeting to answer constituents’ questions, it was well worth the money,” Specter said in a brief interview recently, explaining the origins of the pilot program.

He said he hopes the program will “stimulate” Senators to hold more town meetings. “A lot of people don’t do it,” in part because it is “expensive” to mail the postcards, Specter added.

Critics, and particularly the Toomey campaign, charged from the outset that the pilot program was a $500,000 slush fund intended to help Specter with his re-election.

But it was the supplemental spending bill for Iraq that left them convinced, and ultimately provided one of the more quixotic legislative episodes so far this Congress.

Specter wrote the original law so that mailings would be eligible only for counties with fewer than 250,000 residents — he had, after all, initially justified the program as a way to reach out to constituents in more rural areas, where they may not have very good access to mass media.

Lehigh County, which includes Allentown and serves as Toomey’s political base, has more than 300,000 residents. (The last census put the figure at 314,204.)

A cynic might suggest that if Specter intended the pilot program to help him with his re-election bid, he had blundered, because it would not enable him to hit Toomey in his political base.

That’s when the emergency spending bill for Iraq came along.

President Bush had asked Congress for a “clean” bill, by which he meant legislation that would not include pork projects and other extraneous spending provisions.

Hardly anyone, however, would notice a minor technical correction. Specter, a senior appropriator, slipped in language that struck the 250,000-resident limit from the pilot program.

In the interview, Specter said he found the original language “too restrictive” but did not elaborate. When challenged on it by Pennsylvania media — among other things, they wanted to know why the language was amended in an emergency spending bill for “war” — Specter answered that town meetings with constituents during wartime is a matter of “national security.”

Toomey, who is challenging Specter in the GOP primary from the right, seized the opportunity to suggest the measure was an example of why he is running against Specter in the first place.

“Liberal Senator Arlen Specter has spent a career raising taxes so he can spend money on pet projects,” Joe Sterns, Toomey’s campaign spokesman, said in a prepared statement. “[H]owever, changing the law to waste taxpayers’ hard-earned money on blatant political mail is the height of arrogance.”

Sterns, who has kept tabs on Specter’s movements in the state, said the only other town hall meeting Specter has held since the language was changed in April was in Easton, in Northampton County.

As with Lehigh County, Toomey represents the whole of Northampton. The Census Bureau puts the latter county’s population at nearly 270,000.

It is not clear whether additional Senators have taken advantage of Specter’s pilot program. A full accounting is not likely to become available until at least Oct. 31, by which time the Sergeant-at-Arms and Senate Doorkeeper are required under the original provision to submit a progress report to the Rules and Administration Committee.

Asked whether Toomey’s campaign was justified in charging that the pilot program was intended to help him politically, Specter declined to answer directly.

“I wouldn’t dispute that,” he said. “It’s just not worth responding to.”