Security National Bank, in a hard-hitting response to NS&T Bankshares Inc.'s clarification of its takeover bid, has accused NS&T of misleading Security's shareholders and strongly reiterated its position against the bid.

The letter to the Security shareholders responded to allegations made by NS&T to those same shareholders last week in a separate letter amplifying on its bid to buy up to 100 percent of Security's shares at $62 a share.

Security had said the $62 price was too low in light of its prospects for profitability. But NS&T Bankshares, a proposed holding company for Washington's NS&T Bank (formerly National Savings and Trust Co.), in a letter last week, said the offer "is a very attractive price for your shares" and that the ratio of the $62 offer to the June 30 book value is 170 percent, "nearly twice the average for the last five years."

But Security countered in a letter dated Aug. 29 that "your board continues to believe that $62 per share is an inadequate price for your stock."

Security, to ward off the hostile takeover, announced in July that it would merge with the smaller Washington Bank. That announcement followed Security's rejection of a bid from James Madison Ltd., parent company for Madison National Bank, to pay $60 a share for up to 44 percent of Security's stock.

NS&T, in its letter last week to the Security shareholders, said the proposed merger with Washington Bank wouldn't be as beneficial to shareholders as its own offer. NS&T said the merger would result in a 12.8 percent decrease in shareholders' ownership in Security unless they also owned Washington Bank stock. NS&T also said that Washington Bank ranked among the lowest in its peer group of local banks while Security was among the highest.

However, in its latest response Security said "NS&T Bankshares chose to ignore the dramatic improvement in Washington Bank's performance that has occurred since Leo M. Bernstein assumed control in the latter half of 1980." Bernstein, the principal owner of Washington Bank (formerly Diplomat National), previously was vice chairman of NS&T.

Security stated that NS&T provided shareholders with figures "which merely confirm what we stated to you in our prior letter, namely that Washington Bank incurred net losses in 1980 and prior years" but that those losses created a tax loss carry forward of about $2.5 million, which would benefit Security if it took over the smaller bank.

For the first six months of 1981, Washington Bank has earned $206,344 (34 cents a share).

Security also said NS&T "has raised the spectre of dilution" by stating that Security's shareholders' percent ownership in the merger of Washington and Security banks would drop by 12.8 percent. "What it does not tell you," the Security letter continued, "is that the total capital of the combined bank will increase by the same amount, or 12.8 percent. Thus there will be no change in the book value of your ownership position upon merging with Washington Bank."

Security also included in its letter a form for shareholders who have already tendered shares to NS&T to withdraw them.