Thailand's Democratic Party took a strong lead in parliamentary elections today and indicated it would support a new coalition government to be headed by Prime Minister Prem Tinsulanond.

In television interviews after the polls closed at 3 p.m. yesterday, Democratic Party leader Bhichai Rattakul, currently a deputy prime minister under Prem, appeared to soften his stated opposition to having a nonelected prime minister. Prem, 65, a retired Army general, has not joined any party and did not run in the election but is expected to be returned to office because of his continued support from the military and the royal palace.

The Democratic Party emerged as the biggest winner capturing 101 seats according to unofficial returns, compared to 56 in the last elections, in April 1983. The biggest loser was the Social Action Party, led by Foreign Minister Siddhi Savetsila, which won 43 seats compared to 92 in 1983.

Police said the voting was generally peaceful, although five murders were reported, and two police officers was killed in the crash of a helicopter sent to ferry ballot boxes from an island in the Gulf of Thailand. Police said they had no immediate motive for the murders of four voters and one ballot counter by unidentified gunmen in two southern provinces.

Interior Minister Sitthi Jirarote told reporters that the turnout in the voting for a new 347-seat House of Representatives would exceed 50 percent nationwide, an improvement over participation in 1983.

Democratic Party leader Bhichai indicated he expected his party to join a coalition government with the second- and third-largest parties, the Thai Nation Party, which was expected to win 61 seats, and the Social Action Party, although the latter did less well than expected.