MTA officials have begun testing popular countdown clocks, already in use on most numbered lines, at several stations on the “letter” lines.

The electronic signs have been added at the 14th, 23rd and 28th street stations on the N/R lines as part of a pilot test.

Most stations on the lettered lines — which run on a different operating system than the numbered trains — don’t have countdown clocks because they don’t have sophisticated enough technology.

“They’re the only thing that can help guide you down here,” said Queens straphanger Anthony Bersaud, 36.