Nine days ago, Megan Brennan, the Postal Service's regional vice president, wanted to see for herself the hundreds of overflowing mail bins, rerouted mail trailers and allegedly falsified mail-volume reports at the Southwest Philadelphia mail-processing plant.

When Brennan arrived - in response to the Daily News story on Dec. 1 - the processing plant was ready for her visit, according to a postal-union official.

A trucking firm had just hauled away 19 tons of so-called "waste" mail to be destroyed, said Gwen Ivey, president of the American Postal Workers Union Local 89 in Philadelphia.

"This was workable mail," she said.

Yesterday, Ivey told investigators from the Office of Inspector General about the 38,000 pounds of mail in 36 cardboard 5-foot-cubes, called gaylords, headed for destruction.

More than six special agents and inspectors from the Postal Service's Office of Inspector General are here to investigate potential mail fraud, delayed and destroyed mail and other operational problems here, she said.

Postal workers told the Daily News that they saw first-class mail and pre-paid business-reply envelopes in the gaylords.

Calls to the USPS spokeswoman and the OIG were not returned last night.

In the past 10 days, numerous companies complained to the Daily News that they have not received business-reply envelopes for fundraisers, lab specimens and responses to attend business-related events.

The OIG investigators, who include special agents, a certified public accountant, operations staffers and other inspectors, met with Ivey and four union officials for several hours, asking numerous questions regarding APWU's Oct. 24 complaint.

APWU attorney Nancy B. Lassen said that the agents want to conduct "proffers" with postal workers in connection with the complaint, which alleged that senior managers ordered clerks to undercount the daily mail volume by millions each week, and other issues.

A proffer is an informal meeting with the government in which an individual and his lawyer can disclose criminal activities with some assurance that the information will not be used against the person.

Postal inspectors seized a computer six weeks ago from one of the clerks who had been ordered to lower the mail count, said postal workers, who asked to remain anonymous for fear of retribution.

"Every APWU member has been instructed to cooperate and to answer the truth to any law-enforcement authorities," Lassen said.

Lassen told the Daily News that she expected the federal agents to find evidence of "serious fraud" and other "serious" violations in their investigation.

Lassen said that she would provide investigators with signed statements from union members who have firsthand knowledge of certain activities. *