President Bush told Congress Friday he was releasing a $120 million installment to keep the MX missile program alive but still has not made up his mind on how to modernize the nation's land-based nuclear missiles.

He said the money had to be earmarked to "prevent program disruption" for the 10-warhead MX.The administration is undertaking a review of what mix of next-generation missiles to endorse.

The MX missiles would be deployed in rail cars. A rival plan is to switch to single-warhead Midgetman missiles. Or there could be some mix of the two intercontinental ballistic missile systems.

Bush was initially to tell Congress by mid-February which system he had selected. However, that deadline was missed and the selection - which has been debated for the past ten years - postponed while the review of strategic policy proceeded.

"I am committed to an open and full review of the ICBM modernization issue. I am confident the review will provide the basis for development of consensus on ICBM modernization," Bush said in a letter to the chairmen of the Senate and House committees on appropriations and armed services.

Bush said permitting $120 million to be spent on the MX program would ensure its viability while not endangering the Midgetman program, "which can proceed without additional funds until the national security strategy review and amendments to the fiscal year 1990-91 budget are completed."

"This obligation of additional funds for (the MX) must occur in order to prevent program disruption, substantial cost increases or significant schedule delays," Bush said.