DES MOINES, Iowa (AP) _ Iowa Supreme Court Justice Harvey Uhlenhopp, whose campaigns for court reform led to merit selection of judges, died today after heart surgery. He was 71.

Uhlenhopp, 71, the court's senior jurist, died after a quadruple bypass at St. Mary's Hospital in Rochester, Minn. A spokesman for the hospital said Uhlenhopp had been in poor health, but Chief Justice W. Ward Reynoldson said Uhlenhopp had been more fatigued than anything else.

''It didn't slow him up any. He sat with us in session all last week,'' Reynoldson said.

Uhlenhopp was appointed to the bench by then-Gov. Robert Ray in 1970 and his term would have expired at the end of 1988. A replacement will be appointed by Gov. Terry Branstad after he receives a list of three candidates from the Judicial Nominating Commission.

Uhlenhopp played a large role in the 1962 constitutional amendment that provided for merit selection of judges, Reynoldson said.

Prior to that time, judges were elected, making them subject to the same political forces facing legislators and other elected officials. Reformers said judges should be free to make decisions without fear they might cause political contributions to dry up or induce a strong opponent to run in the next election.

The judges are now appointed by the governor, but must stand for retention at regular intervals. If voters decide not to retain a judge, a new one is appointed. Over the years, only a handful of judges have not been retained.