DUBAI, April 26 (Reuters) - Two Saudi banks soared in early trade on Wednesday after saying they were in initial stages of a merger helping lift the mood in other lenders while shares of Abu Dhabi's TAQA slump after a corporate rating downgrade.

On Wednesday Alawwal Bank agreed to start talks with Saudi British Bank (SABB) about a tie-up that could create the kingdom's third biggest bank with assets of nearly $80 billion.

Shares in Alawwal soared by 9.5 percent, not far off the 10 percent daily limit, after 20 minutes of trade while SABB jumped 6.8 percent.

"While the merger, if it goes through, is good news for both lenders, Alawwal will benefit more from the tie up from reduced operating cost," said Mohammad al Shammasi, chief executive of Riyadh based Derayah Financials.

Most other lenders were also robust, helping lift the Saudi index up 0.2 percent.

Elsewhere, in Abu Dhabi shares of energy company Abu Dhabi National Energy dropped 3.3 percent on news that rating agency S&P had downgraded TAQA's credit rating to 'A-' from 'A' and gave it a 'negative' outlook from 'stable'.

S&P said the downgrade came as a result of "recent related-party transactions at TAQA" which raises "potential risks to our view of the level of government support".

Earlier this month state owned utility company, Adewa, increased its stake in loss-making TAQA, days after it granted the energy company land valued at 18.7 billion dirhams ($5.1 billion).

The Abu Dhabi index, however, was up 0.1 percent with main support from shares of the largest listed company, telecommunications operator Etisalat after it reported a 4.5 percent rise in first-quarter net income from the prior year period to 2.09 billion dirhams, broadly in line with analysts' forecast.

In Dubai, most shares rose with the largest listed developer, Emaar Properties, adding 0.1 percent despite its shares trading ex-dividend on Wednesday.

Shares of Qatar's largest petrochemicals maker Industries Qatar were up 1.1 percent after reporting a first quarter net profit of 928 million Qatar riyals, up 33 percent from the prior year period and above the 866.25 million riyals three analysts had on average forecast the industrial company to make in the period.

The company attributed the rise in profit to higher product prices and improved operating costs.

Doha's index was down 0.2 percent as 11 blue chips declined.

(Reporting by Celine Aswad; Editing by Toby Chopra) ((celine.aswad@thomsonreuters.com)(+9715 62247653)(Reuters Messaging: celine.aswad.thomsonreuters.com@reuters.net))