By Ludwig Burger

FRANKFURT, Nov 6 (Reuters) - German drugmaker Bayer on Monday moved to tap a potentially lucrative new market opportunity for its blockbuster clot prevention drug Xarelto, requesting approval in Europe to make atherosclerosis patients eligible for treatment.

Xarelto is already approved for a number of cardiovascular conditions and prevention of strokes caused by atrial fibrillation, a type of irregular heart beat common among the elderly, is the main profit driver.

The drug, in which partner Johnson & Johnson holds U.S. marketing rights, was earlier this year shown to cut the risk of potentially deadly strokes and heart attacks in patients with severe atherosclerosis by 24 percent, raising the prospects of billions more in sales.

Bayer, which is buying U.S. seed maker Monsanto, has said about 30 million additional patients could potentially benefit from the drug, once regulators give their go-ahead for the atherosclerosis indication.

That would come on top of a population of roughly 25 million patients in atrial fibrillation.

In the irregular heart beat market, Xarelto is head to head with rival pill Eliquis, owned by Pfizer and Bristol-Myers Squibb, and also competes with Boehringer Ingelheim's Pradaxa, but none of them has been tested in the atherosclerosis setting.

The EU filing covers patients suffering coronary artery disease (CAD) or peripheral artery disease (PAD), which are common forms of gradually constricting arteries in the legs, neck and around the heart. They are typically given much cheaper aspirin to prevent cardiovascular knock-on diseases. ($1 = 0.9341 euros) (Reporting by Ludwig Burger)