* Eight countries still need to ratify test ban treaty
* Obama planning new push for pact rejected by Senate in 1999
* China, India, Iran and Israel among others yet to sign (Adds quotes, paragraphs 5 and 10, detail)
JAKARTA/VIENNA, Dec 6 (Reuters) - Indonesia ratified a treaty to ban nuclear weapon tests on Tuesday, a move which the head of the agency set up to monitor the pact said brought it closer to becoming international law.
Adopted by consensus in parliament, Indonesia's endorsement makes it the 156th country to okay the Comprehensive Nuclear Test Ban Treaty (CTBT).
Indonesia had been among nine countries - including nuclear weapons powers the United States and China, as well as India, Pakistan, Israel, Iran, North Korea, and Egypt - whose approval is needed for the law, negotiated in the 1990s, to take effect.
It brought the treaty a "significant step closer to becoming global law", said Tibor Toth, executive secretary of the Comprehensive Test Ban Treaty Organization (CTBTO), in a statement issued in Vienna.
Indonesia's action should create "new momentum" towards the the test ban pact being realised, executive director Daryl Kimball of the Arms Control Association, a Washington-based research and advocacy group, said in a statement.
India, Pakistan, North Korea and Israel are outside the nuclear Non-Proliferation Treaty, the 1970 pact to prevent the spread of nuclear arms. Iran is part of the NPT but the West accuses it of seeking to develop a capability to build atomic bombs. Tehran denies the charge.
Proponents say U.S. ratification of the pact, rejected by lawmakers in 1999, could encourage other holdouts to sign.
"U.S. and Chinese ratification is essential and would prompt action by the other CTBT holdout states," Kimball said. "CTBT ratification by Israel, Egypt and Iran would help reduce nuclear weapons-related security concerns in the region."
The administration of U.S. President Barack Obama said in May that it was preparing a push for approval of the treaty, arguing that Washington no longer needs to conduct such tests but does need to stop other countries from doing so.
But it has not given a precise time when it would seek a Senate vote on the treaty, which the chamber rejected when fellow Democrat Bill Clinton was president in the 1990s. A two-thirds majority would be needed for approval.
"The ratification by Indonesia today will hopefully give a push for nuclear-weapon owners to do the same," Indonesian Foreign Minister Marty Natalegawa said in a statement.
Obama, who will seek a second term next year, has made clear he sees the test ban pact as a step toward his vision of a world without nuclear weapons, such as the new START arms reduction treaty the Senate approved last year.
At the time of the Senate vote 12 years ago, opponents argued that a permanent end to testing could erode the reliability of the U.S. nuclear arsenal. The country last carried out a test nearly 20 years ago.
Some also questioned whether cheaters could be detected. (Reporting by Olivia Rondonuwu in Jakarta; Writing and additional reporting by Fredrik Dahl in Vienna; Editing by Louise Ireland)