Charges against a Harvard sophomore for his part in a rowdy debutante party last summer that caused more than $6000 damage to a Long Island mansion were dismissed yesterday for lack of evidence.

Defense attorneys called approximately 20 character witnesses yesterday in their effort to clear Thomas W. Molyneux '66 and three companions. On two previous days of the trial in Riverhead, L.I., Judge Thomas Stark heard similar misdemeanor charges against three other youths.

If they had been convicted, the seven defendants could have been sentenced to six months in jail, fined $250, or both.

Molyneux had been indicted along with 13 other youths last November by a Suffolk County, L.I., grand jury for willfully destroying property during the early morning of September 1.

He was one of more than 800 guests invited to the coming-out party of Philadelphia debutante Miss Fernanda Wanamaker Wetherill.

After a full night of festivities nearly 100 of the guests--including Molyneux--marched at 6:30 a.m. from Miss Wetherill's home to a neighboring mansion dormitory for the male guests. Accom-that had been rented by the family as a panying the stragglers was a twist band which finally left them at 9:30 a.m.

Breaking, Swinging, and Shooting

It was then that most of the real damage occurred. Until about midday the youths ransacked the mansion breaking all but six of its 1640 windows, swung from chandeliers, and shot at milk bottles with an air rifle.

Last fall Molyneux called the charges against him "completely unjustified" and said that the press coverage of the party had been very unfair.

Mrs. Donald Leas Jr., mother of the debutante, also said then that Molyneux "didn't do anything."

Miss Wetherhill herself testified during the trial and documented many of the acts of vandalism. She recalled how some of the youths had tried to turn a decorative ship's wheel in the mansion and how others had broken one of the beds upstairs.

Of the 14 originally indicted, including one girl, ten have won dismishals, three were treated as youthful offenders, and one is awaiting a trial by jury, which he requested.

The figure of ten dismissals includes all seven defendants who went on trial this week. One had the charges against him dropped on Monday, two on Tuesday, and Molyneux and the three others yesterday.