London — East-bloc countries are making new efforts to block out Western radio broadcasts. The programs are popular among intellectuals, young people, and dissidents.
Recent months have seen new efforts to block or influence Polish and Romanian broadcasts by the British Broadcasting Corporation (BBC) and Polish services of the Voice of America (VOA).
The efforts are part of a heightened sensitivity to all foreign reporting inside the East bloc. Poland and East Germany are both expelling and harassing Western newspaper correspondents. Latest efforts include:
* Jamming of BBC and VOA medium-wave broadcasts to Poland between Dec. 12 and 16, when martial law was suspended and Lech Walesa released, then picked up again for a day to prevent him addressing a meeting.
Only short-wave broadcasts had previously been jammed - and by the Soviet Union. Never before had Poland done the jamming. No one had ever jammed medium-wave broadcasts, which are roughly equivalent to AM frequency broadcasts in the United States.
* Visits by security police to BBC listeners in Romania, who were forced to sign statements saying they would never again write letters to BBC headquarters in London. In some recent years the BBC received some 300 to 400 letters from Romania; last year the total dropped to about 100.
* Expulsion of BBC correspondent Kevin Ruane from Warsaw. The Polish Foreign Ministry did not criticize Mr. Ruane personally, but BBC television here in Britain, and especially the BBC Polish service.
In effect, the efforts point out how the Western broadcasting appeals to Eastern Europeans. But they have also left Warsaw without a BBC correspondent at a time of crucial economic and political importance, and they have put listeners in Romania under sharp new pressure.
For the first time in many years, the BBC has no staff reporter in the Soviet bloc. John Osman has been reassigned from Moscow to London, and the Soviets have held up a visa for his replacement for more than two months.
Meanwhile, the UPI bureau chief in Warsaw, Ruth Gruber, has been expelled, and Polish assistants for other correspondents have been refused new work permits.
In East Berlin, the correspondent for the West German magazine Stern has been ordered out for reporting an assassination attempt on East German leader Erich Honecker.
The medium-wave jamming inside Poland in December (on 231 meters medium wave/ 1296 khz) took the form of Poland's domestic second radio channel being overlaid on BBC and VOA frequencies.
After protesting twice, the BBC received an apology on Dec. 17, claiming a ''generator malfunction.'' The British think the jamming was deliberate, especially since the VOA was also blocked on another frequency.
Six other BBC medium-wave language services were affected for the same period: Bulgarian, Czech, German, Hungarian, Slovenian, and Turkish.
The BBC had been puzzled at the drop in letters from Romania, even on such ''safe'' subjects as rugby and soccer. The first indication of secret police pressure came in a letter smuggled to the West late last year. Now a new emigre to Austria has confirmed it in another letter.
In the case of Mr. Ruane, the Polish government objected to a domestic BBC ''Panorama'' TV program that recreated the early days of Solidarity. In part it used Polish expatriate miners in Pennsylvania for scenes set in a Polish coal mine.
The real target appears to be the BBC Polish service, however. On the air for 33/4 hours a day (up from three hours before martial law was declared at the end of 1981) the service has a high reputation for factual, uncensored reporting.
Warsaw officials are ''uncomfortable that a mass audience in Poland should have access to uncensored information, . . .'' says Douglas Muggeridge, BBC external services managing director.
Polish officials accused the BBC of sending Panorama researchers into Poland posing as tourists, and of smuggling out film. The Poles demand a ''signal'' that BBC Polish service policy has changed.
The BBC refuses to give one - but also refuses to get as tough as the US State Department has been. Last year when the Poles threatened to force New York Times reporter John Darnton from the country, the State Department said the US would expel a Polish journalist. The Poles backed down.
The BBC, saying it respects free access to information, is not asking the British government for retaliation. It merely refuses to support visa applications by Polish journalists, or to help Polish TV and radio men in Britain.
Yet Poland has had no radio or TV correspondent in London since its last man defected in April 1982. The correspondent before him also defected.
The only Polish correspondent here is Tadeusz Jacewicz of the Polish Press Agency. A threat to expel him would hurt the military government, but the BBC prefers to remain low-key.