Sen. Dave Durenberger (R-Minn.) was cautioned by his attorney in 1986 about accepting government reimbursement for stays in a Minneapolis condominium, according to newly available documents, a finding that casts new light on his contention this month that he had no reason to doubt the propriety of the plan.

Durenberger's financial arrangements have been the subject of a 15-month probe by the Senate Ethics Committee, which is expected to decide soon whether he willfully violated Senate rules and deserves punishment.

Durenberger, 55, collected $40,055 in per diem payments from the Senate from 1983 to 1989 for staying in the condominium. He was part owner from 1983 to 1987, and says he sold the facility in April 1987, a deal called a sham by the special counsel for the ethics committee.

The counsel, Robert S. Bennett, argued in trial-like hearings June 12-13 that Durenberger misled the Senate. First, Bennett said, Durenberger hid his part ownership of the condominium as he collected reimbursements from 1983-87; and then he engineered a phony sale to the company owned by his former campaign manager to keep the reimbursement money flowing from 1987 to 1989.

In his appearance June 13, the senator conceded that rules had been broken, but insisted he never intended to commit violations.

It wasn't until December 1989 that Durenberger formally sought the Senate's advice on the propriety of the reimbursements, after a story in the Star Tribune newspaper in Minneapolis raised questions. The Rules panel said $11,005 of the reimbursements were improper, and Durenberger repaid the money. The ethics panel will determine the legality of the remaining $29,050.

Documents made public by the probe show that in late 1986, three years before Durenberger asked for a Senate ruling on the propriety of his arrangements, he was told by his personal attorney, Michael C. Mahoney, that he "couldn't find any support" for the reimbursements the lawmaker had been receiving since 1983. Mahoney recalled the advice in statements to the ethics committee, now part of its official record.