* What: Maruti Suzuki, Tata Motors Sept. quarter earnings

* When: Maruti (Oct. 24), Tata (Oct. 26)

* Robust sales, higher margins to boost earnings

* Higher commodity prices to hit profitability from Q3

Higher passenger car sales in the quarter ended September is likely to boost Maruti Suzuki India (MRTI.BO) earnings, while India's Tata Motors (TAMO.BO) will benefit from a recovery in truck sales, say analysts.

India's top carmaker Maruti Suzuki is likely to report an 86 percent rise in quarterly profit to 5.5 billion rupees from a year earlier driven by higher compact car sales, especially exports of its A-Star hatchback.[ID:nBOM501130]

The automaker, 54.2 percent owned by Japan's Suzuki Motor Corp (7269.T), also benefited from the scrappage incentives in Europe.

Domestic volumes continue to be driven by A2 segment (Ritz, A-Star, Alto, Swift)..., brokerage firm Motilal Oswal Securities noted in a report.

During the second quarter, Maruti's domestic sales rose 22.5 percent to 209,083 units, while exports more than doubled to 37,105 units, data from the company showed.

As the company is operating close to its peak production capacity, analysts say its growth prospects are limited. The automaker's installed capacity is about 1 million cars a month, of which it currently produces 85,000-90,000.

Key concerns arise from (Maruti's) lack of capacity to meet the rising demand, Emkay Global Financial Services noted in a pre-earnings report.

In the July-September quarter, Tata Motors' passenger vehicles sales rose 27 percent, while it saw around 22 percent jump in truck sales, company data showed. Turnover of its light commercial vehicles powered ahead, unlike its high-margin heavy trucks.

Passenger car sales of Tata Motors, India's largest truck maker, were boosted by the launch of its Indica Vista and deliveries of Nano, the world's cheapest car, from July, even though its higher-end Indigo sedan sales declined.

According to Motilal Oswal, a pick up in heavy truck sales as the Indian economic conditions improve would bolster the company's future performance.

Tata Motors' net profit is seen rising by nearly a fourth in the September quarter to 4.3 billion rupees.[ID:nBOM501130]

Brokerage Edelweiss said higher interest and depreciation costs are a cause of concern and could negate the benefits of better operating margins.

While the overall outlook was favourable, higher interest rates and commodity prices and a likely rise in excise duty could negatively impact the firm's profit margins, Edelweiss noted.

Tata's second-quarter earnings would not include that of Jaguar and Land Rover, acquired from Ford Motor (F.N) last year.

Analysts said interest costs from its huge debt burden would also weigh on the company.

Earlier this month, the company raised $750 million through a combined issue of Global Depositary Receipts and convertible bonds, to repay its debt which stood at 240 billion rupees ($5.2 billion) at the end of June.

In the first quarter ended June, Tata Motors' net profit rose 58 percent to 5.14 billion rupees, while Maruti reported a better-than-expected 25 percent jump in net profit to 5.84 billion rupees.

Shares in Maruti, worth $9.4 billion, have risen 59.5 percent during the September quarter, outperforming the main index which has risen 19.4 percent.

Tata Motors' shares, valued at $6.1 billion, have more than doubled during the second quarter.

($1=46.6 rupees)

(Reporting by Janaki Krishnan; Editing by Malini Menon)