Uganda threatened today to take severe measures against U.S. and British residents as a reprisal for "false information" about massacres and torture under President Idi Amin's stormy regime.

Uganda observers said the warning - the second in recent weeks directed at the American community - appeared to be an explicit threat by Amin to take drastic action in response to news reports that he considers critical of his rule.

[In Washington, the State Department said it was looking into the reports that "pressure" would be put on Americans who Ugandan authorities say are putting out information about the country. The United States has no embassy in Kampala and its affairs there are handled by the West German embassy.]

Diplomatic sources in Nairobi said that no specific action appeared to have been taken against the approximately 500 Britons and 100 Americans now in Uganda.

British sources in Nairobi said the Uganda government was apparently annoyed by a report that had originated in Britain, not in Uganda.

The new threat was sparked by an interview in the British Sunday newspaper The News of the World, in which Amin's pilot, Charles Balidawa, said he fled Uganda because of the killing and torture being carried out by Amin's State Research Bureau. The British Broadcasting Corp. carried the report in its international broadcasts.

Radio Uganda denounced Balidawa's charges and said the British and American citizens in Uganda "are the people who are giving false in formation about Uganda to their respective country."

Quoting a government spokesman, the radio said, "The government will bring pressure on the British citizens so they can reveal the source of such false information."

Uganda "will do anything possible to get the truth from these nations," the radio said.

Provincial governors, district commissioners and chiefs were urged to "keep an eye on British and American citizens living in your areas."

Late last month Amin ordered all Americans - mainly missionaries, a few businessmen and airline employees - to remain in the country and ordered them to meet with him. He later rescinded the travel ban and the meeting never took place.

Observers speculated that Amin may have taken the earlier action to try to draw attention from charges that large numbers of Acholi and Lango tribesmen, many of whom are Christians, were being systemtically murdered. The Anglican Archbishop Janani Luwum was among those apparently murdered.

Amin's pilot, Balidawa, was reportedly sent to Britain last month for advanced pilot's training after a plan he was flying made a forced landing in southern Sudan while carrying 16 British guests of Amin's.

Balidawa reportedly waited for his wife and daughter to leave Uganda before applying for political asylum in Britain.