BANGKOK (Reuters) - Thailand's Election Commission on Wednesday endorsed 200 new senators who will replace a military-appointed upper house, revealing a new legislative body that analysts say could make it harder for the embattled ruling Pheu Thai party to govern.

The new upper house will not have a role in voting to approve who becomes prime minister, but will retain the power to vet laws and appoint crucial members of powerful organisations like the Election Commission and the Constitutional Court.

Election Commission Secretary-General Sawaeng Boonmee said that there had been a delay in announcing the results of a complex senate selection process that ended last month because of a number of complaints, which have now been examined.

"The Election Commission has passed a resolution to endorse 200 senators," Sawaeng told reporters.

Provisional results of the senate selection showed an upper house lacking key Pheu Thai affiliates, while marking a gain for its largest coalition partner, Bhumjaithai, which could act as a proxy for the conservative-royalist establishment, analysts said.

A rift between the conservatives, backed by the military, and populist parties like Pheu Thai has long defined Thailand's politics, sometimes triggering violent street protests and military coups in 2006 and 2014.

"The election of a new Senate was a chance to turn a new page and allow a more Pheu Thai-friendly senate to take office," said Mathis Lohatepanont, an independent political analyst.

"This possibility was not realised."

NEW ESTABLISHMENT BULWARK

The new senate, which starts a five-year term this month, also reflects the waning influence of Pheu Thai patriarch and former prime minister Thaksin Shinawatra whose parties have dominated Thailand's politics till last year's election.

Pheu Thai has recently been ensnared in two ongoing legal cases that could see Thaksin jailed and Prime Minister Srettha Thavisin dismissed from office.

Pheu Thai was trounced by the progressive Move Forward in the 2023 elections but the winner wasn't able to take power after it was blocked by the outgoing military-appointed senate.

Instead, Pheu Thai formed the government with the help of rival military-backed parties and others including Bhumjaithai, which was also part of the previous ruling coalition.

Bhumjaithai leader Anutin Charnvirakul, who successfully pushed for legalising cannabis in Thailand last year, is currently deputy prime minister and interior minister.

"Bhumjaithai gained substantial ground and is presenting itself as a new bulwark of the royalist establishment," said Thitinan Pongsudhirak, a political analyst at Chulalongkorn University.

An endorsement from one-third of the new upper house is also required to amend the military-drafted constitution that came in the wake of the 2014 coup. This is a potential obstacle for Pheu Thai, which made an election pledge to revise the constitution.

(Reporting by Panu Wongcha-um and Panarat Thepgumpanat, Editing by Devjyot Ghoshal, Ed Davies)

By Panu Wongcha-um and Panarat Thepgumpanat