Some 5,000 volunteers will take to the streets of Northern Virginia Saturday, going door-to-door collecting funds for the annual March of Dimes Mothers March.

The purpose of the march, organizers said, is to raise funds for medical research to combat birth defects. March of Dimes figures show that more than 250,000 babies, or about one in 12, are born with birth defects in the United States each year.

Many of the birth defects are genetic, including Tay-Sachs disease, sickle-cell anemia, cystic fibrosis and diabetes. Other birth defects are caused by environmental factors, including heavy drinking or smoking by the mother, poor maternal nutrition, and adolescent pregnancy.

"We're asking all the volunteers to call on their neighbors to spread the word about birth defect prevention," said Charlene Baldwin, spokeswoman for the March of Dimes.

In earlier years, the organization has been locked in controversy over the question of abortion, with groups such as the National Right to Life Committee and the Catholic Church urging boycotts because the March of Dimes gives financial support for amniocentesis, which involves extracting amniotic fluid from a pregnant woman's womb and allows doctors to determine whether a baby will be born with certain birth defects. Anti-abortion groups have opposed amniocentesis in the second trimester because they say it serves primarily as a method to identify fetuses that will be aborted.

"We're continuing the same type of boycott that we've had in the past," said Daniel J. Donehey, spokesman for the National Right to Life Committee. "The boycott remains unabated and total."

Spokesmen for the March of Dimes said the group continues to support amniocentesis for diagnostic purposes, but said the March of Dimes does not support abortion.

The March of Dimes, which is not a United Way agency, reports that 85 cents of every dollar it raises is used for research, medical services and health education. The remaining 15 cents is used for administrative and fund-raising expenses.

The march will continue until Jan. 31.