Service on the No. 5 and 6 trains is deteriorating, an MTA official warned on Monday during a board committee meeting.

The two trains only meet the MTA's wait standards 66% percent of the time on weekdays, data shows. Transit officials say an excessive wait is more than 25% beyond what was scheduled.

On weekdays, the No. 5 was only on-time 40.4% of the time, and the No. 6 was at 46.5%, according to MTA data. The performance drops were 4 percentage points and almost 10 percentage points respectively.

Challenged about the late trains by board member Charles Moerdler, MTA officials said the Lexington Avenue subway corridor saw a great deal of ridership growth. They said they focus on wait standards, not on-time performance.

"The 4, 5, and 6, is a very intense line," said Peter Cafiero, chief of operations planning, about the No. 6 train, which has also been challenged by higher ridership and construction work.

MTA officials also said they are changing No. 6 train schedules to make them more accurate, which frustrated Moerdler.

"Just changing the schedule doesn't get the train to the station any earlier, it just masks the problem," he said.