A former U.S. customs commissioner, an Arizona sheriff, the operator of a Tucson drug-treatment center and a disabled World War II veteran came before the Senate ethics committee yesterday at the behest of Sen. Dennis DeConcini (D-Ariz.) to buttress his defense against charges of unethical conduct.

In what appeared to be a full-court press aimed at the committee and his Arizona constituents, DeConcini also introduced letters from four present and former senators attesting to his integrity and the propriety of his conduct in the Senate.

Exploring a chain of events in which DeConcini played a role, the committee also looked again into reimbursements by Sen. John McCain (R-Ariz.) for flights that he and his family took on jets owned or chartered by Keating's now-bankrupt American Continental Corp. (ACC), which owned Lincoln Savings and Loan.

Testifying on the reimbursement issue, former ACC official David E. Stevens said he wrote DeConcini last month to say that he thought the committee was treating DeConcini more harshly than McCain; he reported that DeConcini agreed with him in a return phone call 10 days later.

DeConcini suggested that Stevens submit an affidavit about lack of response to his earlier letter of complaint to committee Chairman Howell T. Heflin (D-Ala.), saying it would show "some evidence was being ignored so that a one-sided case could be presented," Stevens recalled.

Heflin said the letter never came to his notice, and Stevens later said he wished he had phrased some of his complaints differently, including one in which he suggested McCain never intended to make reimbursements for travel by his family.

McCain reimbursed the company $13,433 last year, saying he had been reminded that the flights were not paid for when Keating's office told him the Internal Revenue Service was going to charge Keating for the flights.

DeConcini, McCain and Sens. Alan Cranston (D-Calif.), John Glenn (D-Ohio) and Donald W. Reigle Jr. (D-Mich.) are under investigation by the panel for trying to help Keating at a time when he was raising more than $1.3 million for their political campaigns and causes.

But only DeConcini, singled out by several federal thrift regulators as having offered a deal on Lincoln's behalf at two meetings in 1987, has called character witnesses on his behalf. The first was Sen. Daniel K. Inouye (D-Hawaii) last week.

In testimony yesterday, former customs commissioner William von Raab said he regarded as proper any intervention by lawmakers as long as it violated no laws. He also said he saw nothing wrong with what DeConcini did.

Von Raab said it is common for regulators to meet with lawmakers without aides and even when criminal investigations are threatened, as happened in the "Keating Five" case.

Von Raab acknowledged under cross-examination that he had no direct knowledge of the senators' activities and never faced pressure under the same circumstances.

Later, Rod Mullen, who runs a substance-abuse program, Pima County (Tucson) Sheriff Clarence Dupnik and Earl Bowers, a Disabled American Veterans leader, told of DeConcini's intervention to help cut federal red tape for ordinary constituents who have not contributed to his campaigns.

DeConcini also introduced letters attesting to his character from Sens. Strom Thurmond (R-S.C.), Ernest F. Hollings (D-S.C.) and Paul Simon (D-Ill.) and former senator Robert Morgan (D-N.C.).