Federal bank regulators refused permission last year for National Bank of Washington to sell $15 million of subordinated debentures, bank President Dale Jernberg revealed yesterday.

Answering a question at the NBW annual meeting, Jernberg said the U.S. comptroller of the currency would not permit the proposed capital offering because of "certain things" that had occurred in the bank -- details of which were not disclosed.

Jernberg said bank executives did not think the comptroller's decision had been justified, and he claimed that the top regional officer for the regulatory agency -- Robert Herrmann, based in Richmond -- subsequently had admitted: "We made a mistake."

That recollection promptly was challenged by Herrmann, however. In a telephone interview, the comptroller's official said Jernberg had taken the statement at a Jan. 15 meeting "out of context to a large extent... what I said was that, if the bank decided to float another issue, we would look at in view of changed market conditions" for such an offering.

Herrmann stated that any suggestion about a "mistake" was directed to a change to interest rates -- which have increased dramatically since the NBW proposal was made a year ago with an indicated 9 percent rate. Now, the interest rate on such an offer would be higher.

In addition, Herrmann stated that he was not in a position to judge his agency's action because he had not been involved in the original denial and was "not aware" of what factors led to the Comptroller's action.

Jernberg, who took over as chief executive of the city's third-largest bank last December in a major management shakeup, said after the meeting that the comptroller's office had cited some bad loan situations in earlier years and the resulting absence of a "good running experience" over five years in denying the debenture request.

He told the annual meeting that NBW "probably will refile" a proposed debenture sale "when market conditions change... at some time in the future." While the bank faces no need of additional capital for the "forseeable future," if NBW continues its current growth pace, additions to the capital base will be required.

Last year was the best on record for the 170-year-old institution, with profits up 19 percent to $6 million from $5 million and total resources up 11 1/2 percent to $865 million.

Jernberg forecast yesterday that, because the Federal Reserve Board's efforts to slow inflation growth have not yet been successful, earnings will be affected "in 1979 and beyond."

Stockholders also approved a proposed increase in authorized shares to 2 million from 1.1 million, as well as a 25 percent stock split payable April 16 to owners of record March 20 (the United Mine Workers Union owns 76 percent of NBW's stock).

A proxy statement for the meeting, meanwhile, disclosed new details about NBW loands to a director, John W. Lyon, president of Excavation Construction Co. and of Parking Management Inc. The proxy details some $3.5 million of loans to Lyon business ventures -- not named specifically -- that have been restructured to permit stretched-out payments, as follows:

On Feb. 23, 1977, and original $500,000 loan with an interest rate of 8 3/4 percent was restructured to include an interest charge of the prime rate plus one percent and payment in full by April 1980; the loan balance on Dec. 31 was $310,000, and it was secured by a lien on inventory valued at $1.37 million.

A $2.3 million loan guaranteed by Lyon was restructured in June 1977 with an interest rate of the prime plus 1 1/4 percent, with a final payment due in February 1983; last November, a two-quarter extension was approved. The loan is secured by a lien against marine equipment valued at $2.65 million and a property lien valued at $2.26 million.

Last November, loans to a third firm were consolidated with two loans to Lyon and his wife in the amount of $947,000, with an interest rate of the prime plus one percent and payable quarterly until next Nov. 1, at which time it will be restructued at bank discretion. Stock valued at $3.9 million is pledged against this loan.

The bank stated that, because of terms, all three loan situations may be considered "to involve more than normal risk of collectibility, and may also present other unfavorable features." But the bank expects no losses, "believing the [loans] to be adequately secured."

Lyon's construction company is the focus of several unrelated federal and state probes.