Gillingham clung on for a vital point as Neil Warnock's side missed a hatful of chances.
United, whose unbeaten seven-match league run ended with a 5-1 mauling at promotion rivals Ipswich in midweek, started in positive fashion with Jon Harley twice foiled by Jason Brown.
The ex-Fulham defender, playing in a midfield role, powered in a left-foot drive from 22 yards which was punched away by the Gillingham keeper before Brown had to scamper across the face of his goal to turn away Harley's cross-cum-shot.
United, pushing for an early opener, were caught on the break by lively Mali striker Mamady Sidibe. His low cross from the left evaded the United back four and Darius Henderson stretched but just failed to connect at the far post.
Harley was again involved in the 14th minute after full-back Leigh Bromby slotted the ball neatly into his path, but from the edge of the area the little midfielder fired high over the top.
Danny Cadamarteri, quiet for the opening period, exploded into life on 30 minutes unleashing a ferocious shot from 20 yards which flashed wide of the near post.
Cadamarteri almost found a way through minutes before the interval with a low drive which took a deflection but Brown turned at the last minute to smother the ball.
Gillingham were pegged back in their own half for long periods and had to wait until the 77th minute for another strike at the United goal. Sidibe stretched to meet Andy Hessenthaler's free-kick but from close range he managed to pull his header wide.
Skipper Chris Morgan almost snatched a winner in injury time but his snap shot from 18 yards flashed a fraction wide of the target before Bromby fired in a long-range effort inches over the top.