Four senators have privately urged President Carter not to allow tampering with the board that oversees U.S. radio broadcasts to Communist Eastern Europe or allow former intelligence officials to interfere with or become associated with that board.

The letter to the president by Sens. Frank Church (D-Idaho), Jacob K. Javits (R-N.Y.), Claiborne Pell (D-R.I.) and Charles H. Percy (R-Ill.) reflects a congressional attempt to head off what threatens to become a sensitive issue among the White House, Congress and the State Department.

It would focus on what some souces describe as "a Polish triangle" that has nothing to do with Poland but rather with John Gronouski, chairman of the Board for International Broadcasting (BIB) which oversees the radio stations; Zbigniew Brzezinski, the president's national security adviser and Edmund S. Muskie, the new secretary of state.

The BIB oversees the two U.S. supported and congressionally funded radio stations that broadcast news and commentary in almost two dozen languages to Eastern Europe. Radio Free Europe broadcasts to five of those countries outside the Soviet Union, while Radio Liberty broadcasts exclusively to the Soviets.

The senators say they are upset over the developments: they want the president to keep Gronouski, whose term expired April 30, and not yield to pressure to replace him with candidates who have ties to the intelligence community. Secondly, they are "disturbed" by reports of attempted interference in the board's operation by former CIA officials inside and outside the administration.

Sources say this is a reference to Paul Henze, a former CIA official who is now a member of Brzezinski's National Security Council (NSA) staff and, as a liaison officer between the NSC and the stations, is said by BIB sources to have "very strong feelings" about how the stations should operate.

The matter is especially sensitive because during the 1950s and 1960s, the stations had a heavy dose of secret CIA support. When this was disclosed in 1971, Congress took over the funding and set up the BIB precisely to avoid any such taint.

Since many employes are emigres from the East, the two stations have always been hotbeds of frequently emotional internal debates. Yet the stations have millions of listeners in the East, and have an extraordinary impact on communist populations, well beyond what most Americans realize.

Thus, behind the senators' letter is an effort not to "unleash" the stations toward a more propagandistic role, as some suggest Brzezinski and some others favor.

The BIB has five members, and, aside from Gronouski, two other members -- Frank Markoe and Rita Hauser -- have served out their three-year terms.

No action has been taken on replacements, but sources claim that economist Leo Cherne and University of California professor Paul Seabury are among those have been approached, reportedly by Brzezinski's office, as possible successors. Cherne, in the early 1970s, served on the President's Foreign Intelligence Advisory Board.

In their letter, the senators pointed out that Carter had appointed all the current members, and stressed that the board "as currently constituted has secured the journalistic independence of RFE/RL from all forms of political or bureaucratic interference."

The senators, all members of the Senate Foreign Relations Committee, which must approve board appointments, said they place "the highest importance on continuity."

"We have been disturbed," the letter also said, "by reports of attempted interference in the board's work by former CIA officials inside and outside the administration, and we believe the work of a decade in assuring the professional integrity of RFE/RL would be undone if any of the present members were to be replaced by persons who could even be remotely associated with the CIA or intelligence activities in any capacity."

Congressional sources say there was nothing personal in this aimed at Cherne, or Seabury if he has a similar background, but rather meant to keep anyone with intelligence links out of these jobs.

A White House official said, "Obviously, we will give the senators' views serious consideration," but added that he had "no information or comment on pending personnel matters."

Sources said they expected the issue to come to a head this week and that Muskie, a friend of Gronouski's, is likely to get involved and is aware of the situation. Gronouski left his job as ambassador to Poland in 1968 to campaign for the Humphrey-Muskie presidential ticket that year.