By Lee Jae-won

GOHEUNG, South Korea (Reuters) - South Korea launched its first space rocket on Tuesday but failed to put a scientific satellite into its planned orbit in a setback for the country's nascent space program.

The launch was expected to rile prickly North Korea, which was hit by U.N. sanctions after it fired a long-range rocket in April in what was widely seen as a disguised missile test.

The payload separated from the second-stage booster about eight minutes after lift-off but did not enter its targeted orbit, project officials told a briefing at the space center on South Korea's southern coast, 350 km (220 miles) from Seoul.

"The first stage engine and the second-stage kick motor operated normally and the satellite separated, but it did not put it precisely in the target orbit," Science Minister Ahn Byong-man said.

Officials could not immediately explain what went wrong or what would happen to the satellite, but they said it did not have a booster mechanism to correct its trajectory.

The officials called the project a "partial success" and said they would continue work on a second launch scheduled for next year.

Pyongyang, which chastised the United Nations for the punishment over its rocket launch, said earlier this month it was paying close attention to the South's rocket and how the world would react.

The South's launch came on the second attempt after the scheduled lift-off on August 19 was aborted because of technical problems.

The development of the rocket, the Korea Space Launch Vehicle-1, or Naro-1, depended heavily on Russia's Khrunichev space production center, which built the first-stage booster, conducted tests and provided technical assistance.

The satellite was designed to monitor the Earth's radiant energy.

The Naro-1 was 33 meters (108 ft) long and the two-stage rocket was built at a cost of 502.5 billion won ($400 million).

South Korea wants to build a rocket on its own by 2018 and send a probe to monitor the moon by 2025. It also wants to develop a commercial service to launch satellites.

But its space program lags far behind those of China, India, Japan and to some extent North Korea.

Apart from North Korea, few doubt the South's launch will be for anything but its civilian space program, although it does raise questions about implications for regional security.

Budget and legal constraints will weigh on South Korea even as it tries to move forward with the program, Jane's Intelligence Review said in a report last week.

South Korea's space agency had tried to play down expectations, saying that only about 30 percent of countries' first attempts to put a satellite into orbit succeed.

(Writing by Jack Kim; Editing by Ken Wills and Dean Yates)