MANILA, Philippines - Tensions at the summit of Philippine politics mounted Thursday as presidential frontrunner Benigno Aquino's team vowed to use the "enormous powers" of office to probe outgoing leader Gloria Arroyo.

Arroyo has promised a smooth transition, but she angered Aquino this week by appointing a new Supreme Court chief justice in a move seen as trying to retain influence and secure legal protection after she steps down on June 30.

Aquino triggered their feud when he said Tuesday he would ensure as president that Arroyo was investigated over alleged vote-rigging in the 2004 presidential election, and that suspect government contracts would be reviewed.

Aquino's Liberal Party said he had many options to carry out various probes against Arroyo once he assumes the presidency.

"He has enormous powers as president to lay the groundwork for such investigations," LP spokesman Congressman Lorenzo Tanada told Agence France-Presse.

"He can use the executive branch, which is usually tasked with investigations or ask Congress to do the same."

Arroyo allies have insisted she has nothing to fear from such probes, a stance they repeated again on Thursday as the tensions built.

"Everyone here has a clean conscience," Presidential spokesman Gary Olivar told Agence France-Presse.

Aquino has yet to be officially proclaimed the winner of Monday's election, as an automated tally has slowed down, but his lead is so big over his rivals that most of them have already acknowledged him as the victor.

And Tanada said the Liberal Party was already working to seize control of the influential House of Representatives from Arroyo's allies.

The House was a bulwark of support for Arroyo during her nearly 10 years in power, quashing numerous impeachment attempts and graft investigations against her.

With constitutional term limits meaning she could no longer be president, Arroyo controversially ran for a seat in the lower house and won easily.

Aquino's team worry she could emerge as a powerful force in the lower house, potentially even as its speaker.

The Liberal Party will have only about 50 seats in the new house but it will need at least 150 seats to control it, according to Tanada.

"We will be forced to form a coalition with political parties who believe in the agenda of Noynoy Aquino," he said, adding he expects many of Arroyo's allies to defect now that she is out of power.

"We are looking at these people and getting in contact with them."

Arroyo's decision to appoint Renato Corona, a former chief aide of hers, as chief justice of the Supreme Court on Wednesday, raised suspicions that the president hopes her allies in the court will protect her in any investigation.

Aquino swiftly called on Arroyo to recall her appointment, saying she should respect his right to choose the next chief justice when he takes office.

The Philippine Bar Association, a lawyer's group, attacked the appointment of Corona and threatened to have him impeached.

"He's tainted already. He follows what the incumbent president wants. There's great doubt on his independence and (he is) out to protect the president from suits," said association president Simeon Marcelo.