A key exponent of democratic rule in Nepal, former Prime Minister B.P. Koirala, has been arrested again following his return home from the United States where he had been sent for medical care.

The arrest of Koirala runs counter to a recent trend in the Himalayan kingdom. More than 40 political prisoners have been released in recent weeks following pressure from the United States on human rights grounds and from the resumption of democracy in India to the south.

According to well-informed sources here, delicate negotiations are under way between the the former prime minister and King Birendra over possible movement toward some form of more democratic rule. Koirala still has a following in Nepal and his presence in the country - even in jail - is a factor that the king cannot ignore.

Koirala, 64, and King Birendra, 29, are trying to reach "some accommodation," according to well-informed sources here. Given Koirala's stubborn insistence on democratic processes, observers expect movement in that direction if there is to be any reconciliation at all between the two.

Koirala returned to Nepal last January following eight years in exile in India and was immediately imprisoned on a variety of charges, including inciting armed rebellion.He was abruptly called to the palace in June and told by the king that the royal physicians had found Koirala in urgent need of medical attention for narrowing arteries to the heart. A few hours later, he was on the plane to the United States - all at Nepali government expense.

His re-arrest came last month when he returned.

Observers speculated at the time Koirala left Nepal that the king wanted to avoid the prospect of an outburst by Koirala's followers should the former prime minister become seriously ill or die while in detention. In the background, however, was Koirala's long-time association with Indian leader Jayaprakash Narayan and others who had just overturned Indira Gandhi in the name of democratic rule.

Nepal, situated between India and China, is highly snesitive to outside pressures, particularly from India, through which almost all Nepali imports and exports must travel.

While the India government reportedly has been "correct" in its comments on Koirala, the former prime minister stopped in India on his return and received the outspoken backing of several Indian leaders. He has been criticized vhemently in the Nepali press since his return for having "sold out" Nepali interests.

Meanwhile, the United States reportedly has been quietly making its views known about human rights and political prisoners and these steps are believed to have more than 40 political prisoners, many of them former colleagues of Koirala.

koirala was ousted as prime minister in 1960 by King Birendra's father, King Mahendra, after two years of experimenting with demoratic government. All political parties were banned at the time and remain banned. King Birendra, who succeeded his late father in 1972, rules with the aid of a handpicked Parliament selected under a village-based, or panchayat, system.