NASSAU, BAHAMAS, JUNE 19 -- Prime Minister Lynden O. Pindling's Progressive Liberal Party (PLP) survived a series of drug-related scandals and the toughest electoral challenge to its 20-year rule of the Bahamas today, winning a sixth consecutive term in office.

In unofficial returns broadcast tonight over government-operated radio, the PLP had picked up at least 29 seats, more than enough to control the 49-member House of Assembly and to form a government.

The opposition Free National Movement won at least 13 seats in the balloting, in which an estimated 85 percent of the country's 100,000 voters participated. Two seats reportedly went to former PLP politicians who ran as independents.

The PLP's majority appeared large enough that the party would likely overcome any challenge to its victory based on reports of voting irregularities. Official results are expected Saturday.

Allen Weinstein, president of the Washington-based Center for Democracy, said at a news conference earlier today that "administrative confusion" existed at some voting stations.

Weinstein, who monitored the election at the request of a U.S. Senate Foreign Relations subcommittee, said that some polling places lacked sufficient ballots and that others were delayed in opening because ballots had not arrived.

In a news conference tonight as the results were still coming in, Deputy Prime Minister Clement T. Maynard berated "agencies of the United States" for allegedly interfering in the election on the side of the opposition.

Maynard called Weinstein a "small fry from a university" and, in a challenge to American election monitors, said, "How dare you? We were apalled that someone would be so meddling."

Maynard, who also serves as foreign and tourism minister, declined to specify which agencies he had in mind.

He complained that Miami public relations executive George Depontis had planned the opposition's entire campaign.

Referring to lingering concerns among American citizens and congressmen about corruption in the Bahamas, Maynard declared: "I say to them, go to hell. We're cooperating with antidrug efforts all we can."

Pindling, who returned to his home on Andros Island after voting here earlier, issued no statement tonight.

Although the United States has several bilateral drug-interdiction programs with the Bahamas -- more than with any other country -- American officials have voiced increasing concern that Nassau lacks the political will to curtail transshipments of cocaine and marijuana through this archipelago of 700 islands.

Diplomats and opposition politicians have cited a 1984 report by a Royal Commission of Inquiry that said two government ministers, Kendal W. Nottage and George A. Smith, were involved with drug traffickers. Both ministers were forced to resign but won parliamentary seats by large margins today.

The commission did not accuse Pindling of wrongdoing but found that he had spent $3.5 million -- about eight times his government salary -- over a seven-year period.

Maynard said the elections would serve as the test of popular support for the government in view of the corruption allegations against its members. "The Bahamian people will not support a party that it knows to be even more corrupt" than the PLP, he said.

The results were a surprise to some analysts who had predicted the closest vote here since 1967. That year, Pindling became a national hero by leading his party to victory against a white-minority government.