* Japan orders for eco-friendly cars up 30 pct so far in May
* Has 15 models eligible for green tax incentives in Japan
* Total domestic orders "up slightly" in May
* Shares end up 3 percent

TOKYO, Japan - Nissan Motor Co said on Tuesday orders for its eco-friendly cars are up 30 percent in Japan so far in May from the same period a year earlier, helped by the government's new tax incentives for low-emission cars.

With the addition of the NV200 Vanette light commercial vehicle on Tuesday, Japan's No. 3 automaker now has 15 vehicles in its domestic lineup that are eligible for the tax breaks, Chief Operating Officer Toshiyuki Shiga told a news conference.

Japan lowered taxes on greener vehicles last month in a step the auto industry expects will add 310,000 vehicles in sales in the financial year to March 2010.

To make the most of the scheme, Nissan made improvements in its engines to expand its lineup of eligible cars from the previous six and kicked off a big marketing push for its eco-friendly vehicles.

Including ineligible cars, orders so far this month are "up slightly", a spokeswoman said, adding that the rise was a single-digit percentage.

A climb in May would mark the first increase in Nissan's domestic sales in 10 months.

On Monday, Japanese market leader Toyota Motor Corp said its overall domestic vehicle orders in April grew 20 percent, mostly helped by pre-sale orders for the new Prius hybrid, marking the first monthly rise in orders in two years.

Nissan's Shiga acknowledged that the lack of a hybrid car was a concern it often heard from dealers, but stressed that its extensive offering of fuel-efficient gasoline-engine cars would help lower emissions on the whole at the automaker.

Nissan said it had the highest ratio of cars eligible for a 75 percent tax reduction on fuel-economy standards in Japan.

In the year ended March 31, Nissan's domestic sales, including the 660cc minivehicles it buys from Suzuki Motor Corp and Mitsubishi Motors Corp , underperformed the market with a 15 percent fall.

Last year, Japan accounted for 18 percent of its total vehicle sales.

Nissan's shares ended up 3 percent at 523 yen, slightly better than the transport sector subindex's 2.3 percent rise but lagging Toyota's 3.4 percent rise.