The State Department, citing deep cuts by Congress in the foreign affairs budget, has blocked $50 million to begin construction of a radio transmitter in Israel that would enable the Voice of America, Radio Free Europe and Radio Liberty to broadcast deep into the Central Asian regions of the Soviet Union.

The decision last week by Deputy Secretary of State John C. Whitehead drew a vigorous protest from Malcolm S. Forbes Jr., chairman of the Board for International Broadcasting, which oversees Radio Free Europe and Radio Liberty. RFE/RL, as the jointly run, Munich-based stations are known, had been designated to oversee U.S. participation in the six- to-seven-year construction project that ultimately is expected to cost about $300 million.

In a letter to Whitehead Monday, Forbes recalled that President Reagan had initiated the project in 1984 by sending a handwritten letter to then-Israeli prime minister Shimon Peres. The Washington Post obtained a copy of the letter.

Forbes argued that for the VOA and RFE/RL "the Israel project is the linchpin of a transmitter modernization program that will enable the United States to reach tens of millions of new listeners in the U.S.S.R., Eastern Europe and elsewhere."

He added that the relay station's powerful signal "will contribute enormously to overcome Soviet jamming," which is not used against the VOA now but which has been intensified against RFE/RL.

"Moreover, a failure to act now may result in delaying the project by as much as a full year, which will only increase its final cost," Forbes said.

State Department officials said Whitehead approves of the project and its aims. However, they added, as the official designated by Secretary of State George P. Shultz to identify cost-cutting measures needed to meet Congress' demand for fiscal austerity, Whitehead reluctantly concluded that the radio project will have to wait at least until the administration asks for supplemental appropriations next spring.

The officials noted that Congress is expected to make deep cuts in the administration's fiscal 1988 budget request for $19 billion to cover all foreign policy operations. That, they said, will mean a major shortfall in the amount of money available for foreign aid. Shultz announced Friday that the State Department will have to take a number of austerity measures, including closing two small African embassies and 15 consulates and eliminating up to 13,000 employes over the next fiscal year.

As a result, they said, Whitehead advised the Office of Management and Budget that these parts of the foreign policy budget have been cut so heavily that they cannot afford to divert funds for the radio project.

In addition to the State Department and the Agency for International Development, the foreign policy budget covers funding for the Board for International Broadcasting (BIB) and the U.S. Information Agency, parent organization of the VOA.

The Israelis originally were reluctant to accept the transmitter because of concern that Moscow might retaliate by putting further restrictions on Jewish emigration from the Soviet Union.

However, the Israelis eventually were swayed by Peres' arguments that the Jewish state owed a debt to Reagan and by U.S. promises to spend sizable amounts of the construction costs in Israel.

The original negotiations involved only the VOA. But, by last June, when the U.S.-Israeli construction agreement was signed at a ceremony attended by Reagan, the BIB had been included and designated "lead agency" for the United States on the project.

The VOA, which broadcasts throughout the world in a number of languages, is restricted by its congressional charter to emphasizing news and giving listeners in other countries a picture of life in the United States. By contrast, RFE, which broadcasts to Eastern Europe, and Radio Liberty, which aims at the Soviet Union, are "surrogate" stations intended to counter the government-controlled media of the European communist bloc.

The two stations were created by the Central Intelligence Agency at the height of the Cold War and controlled by the CIA for years.

In the 1970s, Congress consolidated them into a federally funded but private organization under the policy direction of the BIB, whose members are named by the president.

In addition to giving the stations a capability for reaching into Central Asia, the Israeli transmitter will increase their access to most parts of Eastern Europe and to the eastern half of sub-Sahara Africa.