Childhood Lead Poisoning Protection Act of 1998 - Amends title XIX (Medicaid) of the Social Security Act to provide for a reduced Federal medical assistance percentage for States that fail to meet specified minimum blood lead screening rates established by this Act, subject to waiver by the Secretary of Health and Human Services in the case of a State that has performed during a fiscal year such a significant number of lead blood level assessments that the State reasonably cannot be expected to achieve the appropriate minimum blood lead screening rate.

Requires the State Medicaid plan to provide for reporting to the Secretary: (1) the number of children who are not more than two years of age and enrolled in the Medicaid program; and (2) the number and results of lead blood level assessments performed by the State, along with demographic and identifying information consistent with the recommendations of the Centers for Disease Control and Prevention (CDC) with respect to lead surveillance.

Requires each contract between the State and an entity responsible for provision of medical assistance under the State plan to provide for: (1) compliance with mandatory screening requirements for lead blood level assessments commensurate with guidelines and mandates issued by the Secretary through the Administrator of the Health Care Financing Administration; as well as (2) coverage of appropriate qualified lead treatment services, as prescribed by CDC guidelines, for children with elevated levels of lead in their blood. Allows reimbursement for qualified lead treatment services for children with elevated blood lead levels.

Amends the Child Nutrition Act of 1966 and the Head Start Act to mandate lead poisoning screening for an infant or child to be eligible to participate in either the special supplemental nutrition program for women, infants, and children, or early Head Start programs.