Anne Arundel County Executive O. James Lighthizer has vetoed a controversial noise ordinance passed by the County Council last week because the county solicitor said it is unconstitutional and unenforceable.

According to Solicitor Stephen H. Beard, the ordinance would forbid anyone to "yell, shout, hoot, whistle or sing" loud enough to be heard more than 50 feet away at any time--not just between 11 p.m. and 7 a.m. as its author said he intended.

"It could outlaw mowing your lawn on a Sunday afternoon, holding a lawn party or bull roast . . . and whistling while you work," Beard wrote in a memo to Lighthizer.

"How are you going to enforce it when so many everyday activities are affected?" Beard said today. Lighthizer vetoed the law Monday after receiving Beard's memo. It was the first veto by Lighthizer since he was sworn in last December.

Councilman Edward C. Ahern, who wrote the noise ordinance, has said that his intention was to tighten a year-old county law that banned mechanically produced sounds, such as stereo music, between 11 p.m. and 7 a.m. But Beard said the new section is worded in a way that makes it apply at all times and not just at night.

Since the law would apply around the clock and to such ordinary noises as whistling, Beard said it would be impossible to enforce. He said the constitutional issue arises because of the vagueness of terms such as "comfort" and "repose," which are not to be violated by any "unnecessary" noise.

"Those words are so vague it's difficult to know what a violation of the law would be," said Beard. Ahern could not be reached for comment about the veto.