PHNOM PENH, CAMBODIA, JUNE 10 -- The Phnom Penh government, jockeying to retain power after losing U.N.-supervised elections, today formally rejected the results in a move that threatens to undermine a major U.N. triumph here and plunge the country into renewed strife.

At a meeting of representatives of the U.N. peace-keeping mission here and Cambodia's main contending parties, an agitated Prime Minister Hun Sen said that alleged "electoral irregularities" must be resolved before a constitution can be adopted and a new government created under a 1991 U.N.-sponsored peace plan.

Meanwhile, he said, his formerly communist government, installed by Vietnamese invasion forces in 1979, "will stay in place." He also claimed that two top ministers had formed a secessionist movement.

The government's reluctance to accept defeat in May's elections by a royalist opposition party comes even though the ruling Cambodian People's Party would hold the second-largest share of seats in a new parliament.

The U.N. Transitional Authority in Cambodia, the $1.7 billion peace-keeping mission known as UNTAC, is in no position to force a transfer of power, although it fields about 22,000 military, police and administrative personnel in the biggest and most expensive such operation undertaken to date, U.N. officials said. UNTAC's main leverage, the officials said, is to block funding that the Phnom Penh government has requested to pay its civil servants and security forces.

While the government may be bluffing in its bid to retain power, it is playing a potentially dangerous game that could unleash chaotic forces beyond its control, U.N. officials and Cambodian sources said.

Hun Sen asserted today that his deputy prime minister, Prince Norodom Chakrapong, and the minister of national security, Gen. Sin Song, had formed a secessionist movement to press demands for an independent inquiry into alleged voting irregularities and for new elections in several provinces where the ruling party lost or fell short of its expectations.

Chakrapong, 47, is the estranged half-brother of Prince Norodom Ranariddh, 49, the leader of the royalist Funcinpec party. Both are sons of Prince Norodom Sihanouk, Cambodia's figurehead chief of state since 1991, who wants to regain the full powers he lost when he was overthrown in 1970.

Sin Song, like other key leaders of the Phnom Penh government, is a defector from the Khmer Rouge, the radical communist group that ruled Cambodia brutally from 1975 to 1979. He heads the ministry that controls the secret police and covert units charged with sabotaging opposition parties during the election campaign.

"At this moment, a number of provinces have decided to secede and reject the results of the election, and they are refusing to listen to anybody," Hun Sen asserted.

At a news conference, UNTAC chief Yasushi Akashi said there had been "some move on the part of dissident {government and People's Party} elements, who are unhappy with the outcome of the election, to establish some kind of autonomous region in the eastern and northeastern part of Cambodia." He cited the provinces of Svay Rieng, Prey Veng, Kompong Cham, Mondolkiri, Ratanakiri and Stung Treng.

Akashi described the development as a negotiating ploy in government efforts to bargain with Sihanouk and Funcinpec over power-sharing in a transition government.

He said the government could not expect international aid to maintain its administration if it refused to accept the election results, "however painful they may be."

Sihanouk, who chaired today's meeting, expressed fear that Cambodia could split. "This is a tragedy for all of us," he said. " . . . This is a very Third World situation."

In a statement read at today's meeting, Hun Sen said the People's Party "cannot recognize the results of the election as announced by UNTAC." He cited "massive voting irregularities," although the polling was certified by international observers as free and fair.

While the government will not block the formation of a constituent assembly next week, Hun Sen said, the alleged irregularities "must be resolved."

Special correspondent Mary Kay Magistad contributed to this report.