Almost all telephone lines in the Leverett House towers and some lines in McKinlock Hall were knocked out for several hours yesterday afternoon after an industrial backhoe working on St. Paul's lot tore up a 400-line phone cable.

The accident occurred around 3:30 p.m. when the heavy mechanical shovel cut the three-inch underground telephone cable. Construction workers are building two Harvard-owned apartment structures on the DeWolfe St. site.

Repairs on the lines were completed by 6:30 p.m. by New England Telephone management workers, who have conducted repair work during the 14-week strike against the NYNEX Corp. that ended Monday.

Richard Shea, a NET engineer, said the accident disrupted all service in Leverett F-tower. Many students in G-tower also reported that their phones were not working for much of the afternoon.

Leverett Assistant House Master Judith F. Dowling said students had complained that service was disrupted in McKinlock residences as well.

"I was on the phone when it went off around 3:35," Dowling said. "I thought it was disconnected so I hung up and tried to call back but I couldn't."

Dowling raised concerns about the possibility of further problems with work on the St. Paul's site project, which is scheduled to continue throughout the winter.

"We'll just hope it doesn't happen again," Dowling said.