The New York advertising agency that developed the Army's "be all that you can be" campaign -- and then lost the $80 million account 3 1/2 years ago amid charges of bid-rigging and fraudulent billing -- yesterday gave itself a public pat on the back for its work.

In a full-page ad in the New York Times, N.W. Ayer Inc. displayed, without elaboration, a "certificate of achievement" it received earlier this month from a senior Army officer. The certificate mentions Ayer's "exceptional performance and extraordinary contributions" to the Army's recruiting efforts.

Ayer was the Army's ad agency for 19 years, until late 1986, when it was suspended from further business with the government after the Army alleged Ayer had overcharged the service and conspired with subcontractors to submit rigged bids.

The suspension was lifted in mid-1988 and a criminal investigation was dropped after Ayer agreed to pay the Army $750,000 to settle the allegations. Another New York agency, Young & Rubicam, has handled the Army's advertising since early 1987.

An Army spokesman said yesterday that it was "common practice" for outgoing officers to issue certificates of achievement to individuals or organizations that had helped them during their careers. Lt. Gen. Allen K. Ono, the officer who gave Ayer its certificate and who supervises the Army's recruitment advertising, is retiring. Ono sent a similar certificate to Young & Rubicam, said the spokesman, Maj. Joseph Allred.

An Ayer spokeswoman described the certificate as a vindication of the agency's work for the Army. In a letter sent to employees, Ayer Chairman Jerry Siano wrote, "This certificate is ... a distinction and reward for a mission completed with honor by all of us."