* Egypt's market hurt by Commercial International Bank slide
* Saudi's Bupa Arabia jumps on brokerage assessments
* United Arab Emirates markets reopen after two-day holiday
* Dubai Investments continues losing streak
* Abu Dhabi enjoys biggest one-day gain in two years
By Shakeel Ahmad and Abinaya Vijayaraghavan
Dec 4 (Reuters) - Egypt's blue-chip index slumped to an 18-month low on Tuesday, weighed down by Commercial International Bank (COMI) and concern over a proposed law on taxation of Treasury holdings, while Abu Dhabi rose on banking sector gains.
The Egyptian index dropped 2.4 percent, with 26 of 30 stocks falling. The country's biggest lender, COMI, fell for a third straight day, losing 2.5 percent.
COMI and the index have been dented by the proposed legal changes, which could result in a larger tax bill for banks on despite the nominal tax rate remaining unchanged, said Amr Hussein Elalfy, head of research at Shuaa Securities Egypt.
All banking stocks in the index dropped. Several banks have issued statements on the legal changes, with COMI saying they would apply to new Treasury bonds with no retrospective effect and that the tax rate on earnings from Treasuries would stay at 20 percent.
Exchange data on Tuesday showed foreign investors were net sellers of Egyptian stocks, along with Arab investors.
United Arab Emirates markets did not trade for two days because of a national holiday. When they reopened on Tuesday, the Abu Dhabi market added 2.7 percent for its biggest gain in two years. The emirate's largest lender, First Abu Dhabi Bank, added 3.7 percent.
Tuesday is the bank's first trading day after its weighting in MSCI's emerging markets index doubled, meaning that some passive funds linked to the index may have bought the stock on Tuesday. Abu Dhabi Commercial Bank, meanwhile, advanced by 3.8 percent.
Saudi Arabia's index edged down by 0.2 percent, with petrochemicals company Saudi Kayan losing 1.8 percent and Samba Financial Group shedding 1.9 percent.
Health insurer Bupa Arabia for Cooperative Insurance Co surged 7.3 percent after brokerages Morgan Stanley and SICO issued bullish views on the stock.
Southern Province Cement rose 2.3 percent after it signed a contract to sell 20,000 tonnes of Portland cement material to war-ravaged Yemen, where Saudi Arabia has begun working on infrastructure projects in areas it controls.
The Qatar index firmed by 1.5 percent as Masraf Al Rayan jumped by 5.2 percent and Industries Qatar gained 1.5 percent. Doha Bank rose by 4.5 percent after it was included in the FTSE4Good Emerging Index, an index compiled with concern for environmental and social issues.
Dubai's index snapped a six-day losing streak with a 0.3 percent gain. Dubai's largest listed developer, Emaar Properties, climbed 1.8 percent while DXB Entertainments gained 5.1 percent.
However, Dubai Investments lost 4.4 percent after hitting a five-year low in the previous session. The shares have been sliding after MSCI decided to move the stock to its UAE small-cap index from its UAE standard index.
SAUDI ARABIA * The index inched down 0.2 percent to 7,905 points. DUBAI * The index was up 0.3 percent at 2,676 points. ABU DHABI * The index rose 2.7 percent to 4,898 points. QATAR * The index rose 1.5 percent to 10,603 points. KUWAIT * The index rose 0.8 percent to 5,369 points. EGYPT * The index fell 2.4 percent to 12,625 points. BAHRAIN * The index was flat at 1,326 points. OMAN * The index rose 1.9 percent to 4,535 points.
Editing by Andrew Torchia Editing by David Goodman