The Senate ethics committee said yesterday in a final report that it has found no evidence of improprieties that had been alleged in the relationship between Sen. Mark O. Hatfield (R-Ore.) and a Greek financier.

The committee, chaired by Sen. Ted Stevens (R-Alaska), dropped its inquiry last September at the suggestion of the panel's staff. Yesterday's staff report said there was "no credible information" to support any connection between $55,000 in payments from businessman Basil A. Tsakos to Hatfield's wife, Antoinette, and the senator's support for a trans-Africa oil pipeline planned by Tsakos.

The Justice Department still is investigating the matter, and prosecutors recently brought several key witnesses before a grand jury.

The report, which contained considerable conflicting testimony, also included several new disclosures. Antoinette Hatfield told the panel that Tsakos had asked her to be a director of his pipeline company but that she declined. The senator confirmed previous reports that Tsakos had offered him the presidency of the firm.

In one instance of conflicting testimony, however, Tsakos said he made no such offer to Hatfield.

The report also disclosed that Antoinette Hatfield, who received the $55,000 for real estate services, was Tsakos' broker last year in trying to sell his Watergate cooperative apartment for $1.3 million. The original controversy raised questions about whether Mrs. Hatfield had helped Tsakos buy the apartment for about $500,000.

Hatfield said yesterday he is "extremely pleased" by the report's "firm conclusions." Last August Hatfield apologized for his "insensitivity" and donated $55,000 to a Portland hospital. A spokesman said that Mrs. Hatfield no longer is helping Tsakos sell the Watergate apartment.

Four former associates of Tsakos told the panel they believe that the financier's payments to Antoinette Hatfield were intended to influence the senator's support of the $12 billion pipeline project. But the report said that "not one witness provided evidence of any corrupt behavior" on Hatfield's part.

Tsakos' former secretary, Margaret Stocker Chow, said she "suspected that payments by [Tsakos and his wife] to Mrs. Hatfield were made to secure the senator's support for Tsakos' pipeline project rather than for services actually rendered by Mrs. Hatfield."

Chow said the method of paying Mrs. Hatfield "duplicated a procedure previously used by Basil Tsakos . . . in Europe to make payments to individuals whose identity Tsakos apparently intended to conceal . . . . "

H. Robert Ferneau, former vice president of the pipeline company, "testified that he believed that Mr. Tsakos' payments to Mrs. Hatfield were intended to buy the influence of Sen. Hatfield," the report noted. "Ferneau noted, however, that he did not think that Sen. Hatfield 'would have looked at it the same way.' "

Ferneau said Tsakos "had boasted about 'taking care' of Sen. Hatfield and getting what he needed from the senator," according to the report.

Former project director Keith Norman told the panel that he "concluded that Mr. and Mrs. Tsakos set about a program to influence and suborn Sen. Hatfield through Mrs. Hatfield." But Norman said he had "no direct evidence" of this.

The report included a 1981 letter in which Antoinette Hatfield acknowledged the first $15,000 payment from Tsakos "for the work we did in helping you with the purchase of your Watergate apartment."

When questioned about this, "Mrs. Hatfield stated that although she had not shown Mr. and Mrs. Tsakos the specific apartment they bought, she felt the fee was justified because her work in showing other properties allowed the Tsakoses to make an informed judgment on the Watergate apartment they did buy."

Mrs. Hatfield told the panel that she had spent considerable time locating properties for Tsakos and advising his wife on decorating the Watergate apartment. Several witnesses backed up her account, while Chow and others said she played no role in decorating the apartment.

The report concluded that Mrs. Hatfield "did in fact perform real estate-related services" for Tsakos.