LONDON, JUNE 1 -- Britain has prepared a list of possible sanctions against Iran, to be imposed if the Iranian government fails to provide an apology and explanation for the 24-hour abduction and beating last week by Revolutionary Guards of a British diplomat in Tehran.

Iranian officials have said the diplomat, Edward Chaplin, 36, was arrested and has been released only temporarily, pending charges for "serious" offenses, reportedly relating to "drugs, corruption, theft and undermining the economy in time of war."

Foreign Secretary Geoffrey Howe today said the accusations against Chaplin had been "trumped up" in what is being described here as a "tit-for-tat" response by Iran to the shoplifting arrest of an Iranian consular official last month in the British city of Manchester.

"We are not prepared to wait indefinitely for a satisfactory response. The ball is still in Iran's court," Howe said at a news conference in Edinburgh, where he broke off campaigning for the upcoming general elections to deal with the crisis.

Possible British actions reportedly include a severing of diplomatic relations with Iran, a reduction in Iran's 19-member diplomatic staff here or a cutback in British technological exports to Iran, which totaled $600 million last year.

The relative openness with which British officials discussed the situation today and the vigor of their condemnation were seen as indications that London wishes to press Tehran to resolve the crisis before sanctions are imposed.

The major concern here was focused on the still tenuous position of Chaplin, the No. 2 diplomat at Britain's Interest Section that operates in Tehran under the Swedish flag.

On Sunday, Iranian officials told the Swedish charge d'affaires in Tehran that charges were being prepared against Chaplin, who remained today inside the Swedish Embassy compound there.

Howe described Chaplin today as in "reasonably good condition" but "quite shaken" by the ordeal that began with his abduction last Thursday. He was driving home from the British mission with his wife and two small children when a four-wheel-drive vehicle carrying six men pulled in front of his vehicle and abruptly stopped, causing Chaplin to run into it.

When he resisted their attempts to take him away, Chaplin was "severely" beaten, British officials said, and then shoved inside the assailants' vehicle. Neither his whereabouts nor the reasons for his abduction were known until Friday afternoon, when Iranian officials said he had been "arrested for being a suspect" by Revolutionary Guards.

A statement simultaneously issued by the Revolutionary Guards' "Central Komiteh," described by British officials as a morals police and espionage watchdog within the guards organization, said Chaplin had been "temporarily released." Late Friday afternoon, he was dropped off about one mile from his home.

Although Iran has denied that the Chaplin case has any connection to the Manchester shoplifting case, Howe said today that "it's very difficult to believe that they are unconnected."

In her morning campaign news conference here, Prime Minister Margaret Thatcher said, "We shall keep up pressure in Tehran. The charges against Mr. Chaplin we think are outrageous. The matter here is totally unconnected" to the Manchester situation, which she described as "a matter for the police."

The Manchester case began on May 9, when Iranian consular official Ahmed Gassemi was arrested there for allegedly stealing a purse and five pairs of socks from a department store. Released on bail, Gassemi failed to appear at a court hearing May 27. He was rearrested May 28, the same day as Chaplin's abduction.

Iran has claimed full diplomatic immunity for Gassemi, who is a vice consul in Manchester. But Britain repeatedly has said that, under international conventions and the terms of his presence here, Gassemi's immunity is only partial, limited to actions performed in pursuit of his official duties. In contrast, Howe said today, Chaplin is "a fully accredited diplomat entitled to full immunity in every respect."

Tehran has said Gassemi was beaten and "tortured" by Manchester police. British officials have categorically denied that Gassemi was mistreated, but have advised him of his right to register any complaint with police authorities.