WRAPUP 2-Olympics-Phelps goes for eight, Romania wins marathon

* Phelps goes for record eighth swimming gold

* Romania's Tomescu wins women's marathon

* Greek hurdler fails drug test

* Bolt sets athletics programme on fire

By Andrew Cawthorne

BEIJING, Aug 17 (Reuters) - Michael Phelps swims for a record-breaking eighth gold at one Games on Sunday in Beijing where spectators are still agog at Usain Bolt's 100 metre win.

The first gold of Olympics day nine went to Romania when Constantina Tomescu crossed the finish first in the Bird's Nest stadium after a marathon run that began in Tiananmen Square.

Catherine Ndereba of Kenya took silver and Zhou Chunxiu of China the bronze, with Britain's world record holder Paula Radcliffe struggling with fitness and well back.

In the highest-profile doping case yet of the Aug. 8-24 Games, Greece's defending women's 400 metres hurdles champion Fani Halkia failed a drug test hours before she was to compete.

That recalled the doping sagas that darkened Athens 2004.

But it has been the scintillating sport not scandals in Beijing dominating attention and relegating the pre-Games focus on China's rights record and pollution problems.

Having matched fellow American swimmer Mark Spitz's seven golds at Munich 1972, 23-year-old Phelps will stand alone in the record books if he and team mates win the men's 100 metres medley.

Phelps' 13 golds, which include six in Athens, make him the most successful Olympian of the modern era. A second-string U.S. squad qualified fastest in the medley heats, setting up Phelps and his "A-team" colleagues as firm favourites in the Water Cube.

Phelps has failed to match Spitz in one aspect.

His fingertip win on Saturday in the 100 metre butterfly over Serbia's Milorad Cavic was not in a world record time, unlike his six previous wins in Beijing.

All seven of Spitz's medals came in world record times.