It is one of the most critical calculations in designing any skyscraper: can the building withstand the tremendous forces created by the wind that accompanies the worst possible hurricane?

The engineers who designed the twin towers, it turns out, made them exceed the wind load requirements in New York City codes, investigators at the National Institute of Standards and Technology said in a statement posted on their Web site on Friday.

Federal investigators studying the World Trade Center collapse have spent months researching and recalculating this question for the twin towers, to determine whether the original design might have played a role in what happened on Sept. 11, 2001.

The towers' capacity to handle extreme wind loads became critical on the day of the attack because this wind force threshold determines the upper limit of a building's strength.

In June, investigators from the agency, which is a division of the United States Department of Commerce, said they were unsure whether the wind-force calculations for the twin towers had been adequate.

The doubt surfaced when tests conducted after the attack found that winds that might hit the twin towers in the most extreme storm were stronger than what had been anticipated in data published by the Port Authority of New York and New Jersey in the 1960's, when the towers were built.

On a normal day, a skyscraper has much more capacity to support its weight than it needs. When the two planes hit the towers, knocking out many exterior columns and starting fires that weakened others, this reserve capacity determined, in large part, how long the towers stood.

The somewhat conflicting information about wind forces and the twin towers design is not surprising, said S. Shyam Sunder, who is overseeing the institute's investigation.

It demonstrates what Dr. Sunder said he believed might be insufficient standards for how to conduct wind tunnel tests and calculate wind loads. Different testing laboratories that engineers rely on can often produce different results.

''This is something we need to pay greater attention to,'' Dr. Sunder said, adding that it is likely to be one of the recommendations in the final report by the institute on the trade center collapse. A draft of that report is due in December.