The nation's maternity health system is "fundamentally flawed" with nearly one-third of all U.S. babies being born to mothers who receive insufficient prenatal care, a panel of medical experts warned Tuesday.

In a 254-page report, a National Academy of Sciences committee said just 68 percent of pregnant women obtained timely and adequate prenatal care in 1985.Although use of such care rose in the United States from 1969 to 1980, the 10-member panel found the percentage of women receiving it has remained stable or has declined since 1980, particularly among blacks.

Indeed, one of the report's most troubling findings is that since 1980 there has been a marked increase in women receiving late care or none at all. From 1981 to 1985, the last year statistics were available, the percentage of black births falling into that category rose from 8.8 percent to 10.3 percent.

The committee defined adequate prenatal care as medical attention that begins in the first three months of pregnancy and includes nine or more visits before birth. Late care does not begin until the pregnancy's final three months.

"The data reveal a maternity care system that is fundamentally flawed, fragmented and overly complex," the experts wrote. "Unlike many European nations, the United States has no direct, straightforward system for making maternity services easily accessible.

"Although well-insured, affluent women can be reasonably certain of receiving appropriate health care during pregnancy and childbirth, many women cannot share this expectation," they added.

The report cited teens, low-income women, inner-city and rural residents and uninsured or underinsured females as those "likely to experience significant problems in obtaining maternity services."