Child-care centers would be opened at up to eight Metro stations or other Metro facilities in the District, Maryland and Virginia under a venture approved yesterday in an effort to build ridership by appealing to working parents.

The transit system board also agreed yesterday to postpone the opening of the first three Green Line stations by a week, until May 11, to avoid conflict with another celebration in the District.

Under the experimental child-care plan, Metro will consider one proposal each from its eight member jurisdictions. Local governments would operate centers or contract with private companies to run them on land at or near transit facilities.

Metro would provide the space -- vacant land, parking lots or nearby property slated for joint ventures with developers -- free or at low cost. Metro would not build or operate the centers or otherwise be involved. The cost to Metro would depend on the value of the contributed land. Transit system officials said a study showed that 34 of its 74 current or soon-to-open rail stations have suitable space.

The first center to open could be in Montgomery County, which already has asked the State of Maryland for bond money to help build a center for at least 100 infants and preschoolers on vacant land next to the Shady Grove station.

Jackie Townes, the county's child-care division marketing director, said the center could open in three to five years, and may include room for elementary school students during the summer.

The experiment is "an innovative approach to providing additional child care," said Metro board member Mary Margaret Whipple of Arlington, the proposal's chief sponsor.

The child-care experiment was pushed by Rep. Frank R. Wolf (R-Va.), who sponsored a request in Metro's congressional appropriation last year for two child-care centers at Metrorail stations, one each in Virginia and Maryland.

"This effort will create new child-care spaces, and that will help everyone who lives in the Washington region," Wolf said in a statement.

The Washington area has the nation's highest percentage of working mothers, with 72 percent of women with children under 14 employed. At the same time, Metro officials said, surveys show many families are dissatisfied with their child-care arrangements.

The quick vote to approve the plan at yesterday's board meeting followed months of debate on Metro's reluctance to get involved in ventures not related to mass transit. The board went through similar discussions before approving proposals to sell stamps at its stations and install money-card machines.

Beverly Silverberg, spokeswoman for the transit authority, said all eight of Metro's jurisdictions are interested in sponsoring child-care centers.

The Green Line vote will affect the Mount Vernon-UDC station at Seventh and M streets NW, the Shaw-Howard University station at Seventh and S streets NW and the U Street-Cardozo station at 12th and U streets NW.

The delay in opening the Green line stations was applauded by residents and business owners along the Seventh Street and U Street corridors. They had objected to the initial May 4 date because local school bands were committed to marching in an annual school patrol parade and would not be available for the Metro opening.

The board has not yet selected a station to be the site of the official opening.

Community leaders near the Shaw and U Street stations have requested that the ceremony be held in their neighborhood.