* Dos Santos offers to alter bid for PT holding company
* Statement follows criticism of bid from PT assets owner Oi
* Dos Santos aims to block sale of PT assets to Altice (Recasts with statement from dos Santos)
By Sergio Goncalves
LISBON, Nov 11 (Reuters) - Angolan investor Isabel dos Santos said on Tuesday she was willing to change the terms of her bid to buy Portugal Telecom if necessary, to prevent Brazil's Oi from selling PT's assets to a rival party.
Dos Santos launched the bid for Portugal Telecom, a holding company with a 25.6 percent stake in the combined Oi-PT company, partly in an attempt to thwart a 7 billion-euro bid for PT's Portuguese assets by French telecoms group Altice .
Oi is merging with Portugal Telecom but has already signalled it would consider selling its partner's operations in its home market, enabling it to pay down debts and invest in the Brazilian market.
Oi said on Tuesday the bid by dos Santos - who is the daughter of Angola's president and Africa's richest woman - was "unacceptable" as it would affect the terms of the merger.
But dos Santos shot back, saying she is willing to change some terms of the offer to convince shareholders and address Oi's concerns. Success depends on PT's shareholders, not Oi; PT has two members on Oi's board who could veto any potential sale of PT's assets by Oi.
"We believe strongly in this project and if we can gather support to make it possible we will do everything possible to make it happen," dos Santos' spokesman for her Portuguese company Terra Peregrin told Reuters.
"This is a value-creating proposal that involves Oi and its shareholders that will enable Portugal Telecom to remain a single company, avoiding the dismantling of the Portuguese company," he said.
Shares in Portugal Telecom were 5.36 percent higher at 1.4340 euros a share Tuesday afternoon - above the offer price.
"The likely change of the bid terms is positive although it does not mean the price is revised... The market is expecting a price revision or a rival offer, and on the other hand, it expects Oi's price to keep rising," which helps PT's share price, said Albino Oliveira, an analyst at Fincor brokers.
The merger between Oi and PT soured over the summer when PT said it had loaned 900 million euros to the Espirito Santo banking family, which subsequently went bankrupt. The merger conditions were then revised, giving PT a smaller portion of the combined, new company.
After that Altice, which is controlled by Franco-Israeli billionaire telecoms entrepreneur Patrick Drahi, offered to buy the Portuguese operations of Portugal Telecom from Oi for 7 billion euros.
Brazilian daily Valor reported on Tuesday that Oi shareholders are in Lisbon to consider the bid by Altice.
If Oi were to sell Portugal Telecom's assets to Altice, it would effectively unwind their merger that was unveiled last year and was supposed to create a stronger company. If dos Santos succeeds in her bid, she could potentially pay off the Espirito Santo debt and increase her stake in Oi to 38 percent.
Among the main shareholders in the PT holding company are Novo Banco - the 'good bank' carved out of bankrupt Banco Espirito Santo in a 4.9 billion euro bailout this summer - and Portuguese investment fund Ongoing.
Together with Portuguese conglomerate Sonae, dos Santos controls Portugal's second-largest telecoms operator NOS . (Additonal reporting By Andrei Khalip; wrting by Axel Bugge; editing by Sophie Walker and Philippa Fletcher)