LONDON (AP) _ KGB chiefs told their CIA counterparts last week that foreign hostages in Beirut are alive but in dreadful condition and are frequently drugged by an Iranian physician, a British journalist reported Sunday.

Gordon Thomas said in an article in The Sunday Express and in an interview on Independent Radio News that Soviet and American intelligence chiefs met twice during the Washington summit.

He cited unidentified sources in the U.S. Central Intelligence Agency, Israel and the Middle East.

In Washington, a senior White House official was asked to comment on the report and he said he was ''unaware that any such discussions had been undertaken'' between the KGB and CIA. The official spoke on condition he not be identified.

A radio station in Beirut said Sunday that a close aide to Iran's Ayatollah Ruhollah Khomeini is in Lebanon on a mission linked to the plight of foreign hostages held by pro-Iranian Shiite Moslem extremists.

Thomas said the intelligence sessions, attended by the CIA's director of operations and the head of the KGB's Middle East desk, represent ''a dramatic breakthrough because ... the Americans have persuaded the Russians to bring their considerable weight and authority to bear on the Shiite Moslems.''

The Soviets told the Americans that Dr. Ibrahim al-Nahir was ''managing'' the hostages with drugs so they can be easily interrogated and moved without making a break for freedom, he said.

Thomas said the physician has been working in Beirut for three years for the pro-Iranian Shiite fundamentalist group Hezbollah.

The Soviets said those under al-Nahir's control include Anglican envoy Terry Waite, who disappeared in Beirut last January while trying to negotiate the release of Western hostages, Thomas said. he said Waite is being held in the Fakhani neighborhood of Moslem west Beirut not far from the Soviet Embassy.

No other hostages were mentioned by name.

''The Russians were able to confirm that the position of the hostages remaining in Beirut was quite dreadful. Under this Dr. al-Nayer, they are hooded, manacled to the wall as (former American hostage) Charles Glass was ... They are often kept in isolation for lengthy periods. But what is most terrifying of all is the CIA has been told from their Soviet counterparts that Dr. al-Nahir has frequently drugged the hostages,'' he said.

Excluding Waite, 20 foreigners are missing after being kidnapped in Lebanon, including eight Americans. The longest-held is Terry Anderson, chief Middle East correspondent for The Associated Press, kidnapped March 16, 1985.

Thomas spent the past year in the Middle East researching a book on medical terrorism. He told the AP he was a longtime friend of William Buckley, the CIA station chief in Beirut who was taken hostage and killed.

Dr. Ariel Merari, an expert in terrorism at the Jaffe Center for Strategic Studies in Tel Aviv, was quoted in The Sunday Express article as confirming the report on the role of al-Nahir, a 35-year-old graduate of the Tehran University Medical School.

''From what we know of the way the hostages are treated, there is no question at all that Dr. al-Nahir is guilty of torture,'' Merari was quoted as saying.

The Christian-controlled Voice of Lebanon radio station said without attribution that Ayatollah Sadek Tabatabai, an aide to Khomeini, arrived in Beirut on Friday with a mandate to ''discuss the issue of foreign hostages.''

It also said unnamed Tabatabai aides recently opened an office in Geneva to follow up the cases of foreigners kidnapped in Lebanon.

Reporters based in the city of Baalbek, in east Lebanon, said Tabatabai has met with unidentified leaders of Hezbollah, or Party of God, in eastern Lebanon.

Hezbollah is believed to be an umbrella organization for pro-Iranian Shiite groups said to be holding most of the foreigners missing in Lebanon.