Most of the bombs dropped by U.S. warplanes on Iraqi radar stations during last week’s airstrikes missed their mark, said Pentagon officials, with most of the misses blamed on a new and expensive Navy guided bomb. A Navy official said about 25 of the guided bombs, which were first used in combat two years ago, were dropped in the attack, and the majority fell “tens of yards” from their targets. Another official said he had been told the bombs missed by an average of more than 100 yards. Pentagon officials’ assessment of Friday’s airstrikes against the Iraqi anti-aircraft system, which involved U.S. and British warplanes, was initially glowing. But the disclosure of the guided weapons failure rate stunned defense officials yesterday and led them to scale back their assessment of the damage done in the attack.