Education Secretary William J. Bennett said yesterday that American children are suffering educationally because of the breakdown of the traditional family, citing his own childhood in a single-parent home to point up the difficulty single parents have in raising children.

"The decline of the traditional American family constitutes perhaps the greatest long-term threat to our children's well-being," Bennett told community groups at the Omni Shoreham hotel.

"Take one of the parents out of the home and the educational health of the child is likely to suffer," he said. "Children from single-parent homes are more likely to have lower grades, more likely to be discipline problems in the classroom, more likely to skip school, more likely to be expelled, more likely to end up as dropouts. They are more likely to experience emotional or psychological disturbance, more likely to become involved with drugs, and more likely to get in trouble with the law."

Bennett did not cite any research to support his contention.

He said there are many exceptions to the rule, including himself. But when his parents divorced, his mother raised two children alone and "it was obvious to me, it was obvious to my mother, that it is much harder for one parent to raise a child than it is for two . . . . It is simply a matter of spreading oneself too thin."

He is the latest administration official to speak of what they call a "crisis in the family," in advance of a report by the presidentially appointed Working Group on the Family, which is chaired by Bennett's undersecretary, Gary Bauer. The report is due in November.

U.S. Census Bureau figures show that the "traditional American family" often praised by Reagan administration officials may be a vanishing breed, with single-parent families representing 11 million of 61 million total family households. About 10 million single-family households are headed by women. Also, census figures show that more than 20 percent of American children now live in single-parent homes.

Bennett noted the increase in homes headed by women and asked: "Where are the men? . . . many are not with their children."