When 69-year-old Robert Bennett, of Chesapeake City, Md., heard over the telephone that he had won this year's Irish Sweepstake's "super prize" of $680,000, he asked that each number be read over the phone before he believed he had won.

The father of five, and a horseman since he left Ireland 47 years ago, Bennett said he "found it hard to believe for the first five minutes, but the caller kept saying 'no question about it you're rich.'"

Bennett is the manager of a horse farm that has 200 mares and 11 stallions. This week his chief concern has been that several mares are about to give birth.

Bennett also now holds the distinction of being the last season to win such a large amount from the fabled sweepstakes. The top prize is to be reduced next year to $425,000.

"The first thing that burst into my mind is that we now have some security. I've been working all my life and I've never been out of a job since the 1930s," said Bennett. He insisted he "wasn't that excited" about the news but his wife Elizabeth disputed him. "My husband pretended to be very nonchalant about it, but he was just as excited as I was," she said.

The Bennetts, whose children are married and living away from home, said they do not plan to alter their conservative life style.

"He may want to own his own farm," said Mrs. Bennett, "but that is about as far as he will go."

Bennett, who had spent yesterday caring for the mares, said: "We are going to be realistic about this and not going to throw this money around."

Bennett said he is not going to "walk out" on the owner of the horse farm because of yesterday's windfall.

A trip to Ireland, however, which was planned some time ago by the Bennetts, will have an added feature. Bennett says he plans to talk to his "tax man" and find out just how much money he should bring back from that country.

"I think we will probably have to get the prize money over a period of five years."

Bennett said he had just received his sweepstakes tickets several days ago from his sister Grace Long of Mungret in County Limerick, Ireland. She had bought the ticket for her brother and sent it by mail.

When their children heard about the winning, Mrs. Bennett said: "They were ecstatic. They were all up in the air about it. Now they all want to go to Ireland."

The lottery is operated by Irish hospitals as s fund raising tool, and many tickets are sold to United States citizens.