By Alan Baldwin

LONDON (Reuters) - Katherine Grainger, Britain's most successful female Olympic rower, still has a chance of making her fifth Games despite being left out of an initial squad of 43 named for Rio on Thursday.

The British Olympic Association (BOA) kept the door open to the 40-year-old by deferring a decision on a further four rowers including those who will compete in the open women's double sculls.

Grainger won gold in that event at the London 2012 Games with now retired partner Anna Watkins.

The Scot switched her focus to the women's eight in May after she and double sculls partner Vicky Thornley, 28, failed to make the podium in that event at the European championships and disbanded.

Neither was selected for the eight but British Rowing performance director David Tanner indicated Grainger and Thornley were likely to be reinstated in the doubles boat.

"There are one or two steps before we get there but very, very soon," he said.

Grainger, a four times medalist with a gold and three silvers, is Britain's most successful female Olympian in terms of medals along with retired swimmer Rebecca Adlington.

Those named on Thursday included defending women's pair champions Helen Glover and Heather Stanning.

Alex Gregory, a men's four gold medalist in 2012, is joined in that boat by Mohamed Sbihi, George Nash and Constantine Louloudis. The latter three were all bronze medalists four years ago in the men's eight.

Under Juergen Grobler, the former East German coach who moved to Britain in 1991 and has coached crews to gold at 11 Games since Munich in 1972, the British men have won the coxless four at the last four Olympics.

Katherine Copeland, who won the 2012 lightweight women’s double scull gold with Sophie Hosking will try to defend her title with Olympic debutante Charlotte Taylor.

Frances Houghton is set for her fifth Olympic Games appearance in the women's eight.

Rowing is one of Britain's strongest Olympic sports, with the country top of the medals table at the 2012 regatta with a total haul of nine including four golds.

Tanner said Britain had a target of six medals this time.

(Reporting by Alan Baldwin, editing by Clare Lovell)