Prime Minister Margaret Thatcher arrived in Bangkok Saturday for the first official visit to Thailand by a British head of government in 376 years of diplomatic relations between the two countries.

Arriving just ahead of a monsoon storm, Thatcher and her husband, Denis, were greeted by two Thai prime ministers - acting Prime Minister Prem Tinsulanonda, who formally left office two days before, and new Prime Minister Chatichai Choonhavan.He was officially appointed prime minister by King Bhumibol Adulyadej on Thursday following Sunday's elections but said Prem would continue to serve as acting prime minister until his cabinet takes office - probably Tuesday.

Thatcher completed her review of a Thai military honor guard and entered a reception hall only moments before a monsoon rainstorm broke, drenching those still on the airfield.

Thatcher, on the last stop of a 12-day visit to Asia and Australia, is scheduled to spend four days in the kingdom whose relations with Britain date back to 1612 when British traders presented credentials from King James I to Thai King Songtham.

Relations became much closer with a treaty of "Amity and Commerce" in 1855, but until Saturday no British prime minister had ever visited Thailand.

Thatcher is scheduled for an audience with King Bhumibol Adulyadej, talks with Chatichai and with outgoing Prime Minister Prem Tinsulanonda.