Somerset trailed Lancashire by 313 runs with seven first innings wickets remaining when rain halted play at the County Ground in Taunton.
Morning rain prevented play getting underway until 1.10pm and it took the Lancashire batsmen just seven balls to move from their overnight total of 395 for nine to 400 and earn themselves maximum batting points when Kyle Hogg took a single off Vernon Philander.
Without further addition to the total, Philander accounted for Simon Kerrigan, caught at gully by Arul Suppiah, to give Somerset maximum bowling bonus points.
Philander ended with figures of five for 71 from 24.3 overs, his second five-wicket haul in three championship games.
At the start of their reply Somerset openers Arul Suppiah and Lewis Gregory, deputising for the injured Marcus Trescothick, found runs hard to come by against the accurate Lancashire opening attack of Glen Chapple and Hogg.
Gregory had moved onto 15, out of 17 on the board, when he edged the first ball of the 11th over of the innings, bowled by Chapple, to Paul Horton at first slip.
Chapple struck again in the 17th over when he bowled Suppiah, looking to drive, to leave Somerset 28 for two.
James Hildreth joined Nick Compton at the wicket and opened his account with a crisply driven cover drive off Sajid Mahmood.
The third-wicket pair started cautiously but after playing themselves in, Hildreth brought up his side's 50 with two off Mahmood to midwicket in the 24th over.
The partnership was worth 53, when, with the total on 81, Hildreth was leg before wicket to Luke Procter, looking to turn the ball to leg, for 30.
Two overs after the interval the rain started to fall again and the players left the field with the score on 87 for three, after which they did not return, by which time Compton was unbeaten on 30 off 83 balls, bringing his first class total for the season to 715, while Craig Kieswetter ended four not out.
For Lancashire, Chapple ended the day with figures of two for 15 from his 11 overs.
The third day's play was finally abandoned at 6pm with less than 40 overs completed.
