The Mark O. Hatfield Clinical Research Center at the National Institutes of Health in Bethesda, Md., one of the country's largest health-care projects currently under construction, is moving toward completion in 2003. The 850,000-sq.-ft. addition to the 43-year-old clinical center will replace outdated facilities and upgrade research capabilities. Architect for the project, which has a cost of $360 million, is Portland, Ore.-based Zimmer Gunsul Frasca Partnership. Dallas-based Centex Construction Group, under a contract with Boston Properties, became the project's construction manager this summer. Original contractor McCarthy concluded its work in May after it and Boston Properties were unable to agree on a guaranteed maximum price.