A SET OF FACTS strung together in a story by a Cox Newspapers reporter, and played very large in this paper July 3, raised suspicions of possible conflicts of interest or other improprieties involving Sen. Mark Hatfield (R-Ore.), his administrative assistant and the U.S. National Bank of Oregon.These have been rejected by the Senate Ethics Committee - and properly so, in our opinion.

The Hatfield case is interesting in part because it illustrates a recurrent problem: How much information is needed to make sound judgments in the ethics field? These were the unadorned facts: The senator had gotten a large mortgage on a Washington house from a bank in his home state; a few months later, his office interceded with a regulatory agency in behalf of the bank; in addition, his top assistant happened to be a director of that bank. Before you leap to any judgment, you need to consider that there are a lot of facts missing from this story that would be crucial to a demonstration of any wrongdoing.

For example, the July 3 story did not include evidence of any explicit connection between the loan and the aid for the bank. It did include considerable detail bearing on the key question of whether public business and private interests might have been mingled improperly. First, the $420,000 loan to Sen. and Mrs. Hatfield was not unsecured; it consisted of a $200,000, 25-year mortgage on the home they were purchasing, and a $220,000, 21-month second trust secured by four other properties that the Hatfields already owned.

Second, when the bank vice president asked Sen. Hatfield's aide, the bank director, to help with a matter pending before the Comptroller of the Currency, the aide did not rush to take care of it himself. He simply referred the case to other staff members without any recommendation at all. They drafted a letter asking the acting comptroller to defer a decision, signed the senator's name - in accord with standard office procedure - and sent the letter without even telling Mr. Hatfield about the case.

Those details make the events sound more coincidental and innocuous. It may be debatable whether a top aide to any legislator ought to be on the board of a major home-state bank, but beyond that the situation seems simply to reflect the type of juxtaposition that is inevitable as long as senators and their staff 1) have any personal financial interests at all, and 2) do routine casework for constituents.

That is roughly where the Senate Ethics Committee came out. The panel looked at the news report and at financial and other information tht Sen. Hatfield volunteered and saw no violation of the Senate ethics code. Lacking a sworn complaint from anyone, the committee decided to let the matter rest.

Those who take a dim view of congressional ethics may argue that there could be much more to the mater and that the committee should not have set it aside so fast. In our view, however, the panel's decision was sound. The available information is ample and reasonable enough to support the conclusion that nothing utoward has occured and, indeed, that everyone involved has acted properly. To keep worrying such cases, out of nothing more than general mistrust o human motives, strikes us as grossly unfair to individuals such as Sen. Hatfield. It can also divert attention from the real problems of official ethics that do persist.