James A. Hagen, who has been described as one of the principal architects in the creation of Conrail, is leaving his position as a senior vice president at the government-owned railroad to fill the new post of executive vice president for marketing at CSX Corp.

In the new position, Hagen will direct CSX's efforts to merge the marketing operations of the Richmond-based company's two rail subsidiaries, Chessie Systems and Seaboard System Railroads. CSX, which was formed in 1980 by the combination of the two railroads, still runs them as largely independent networks.

The appointment comes as Congress is considering a proposal by the Transportation Department to sell its 85 percent share of Conrail to Norfolk Southern Corp., CSX's principal competitor. CSX, which originally wanted to split the government-owned railroad with Norfolk Southern, has argued that an acquisition of Conrail by Norfolk Southern would be anticompetitive.

Hagen's move, however, is not related to the proposed sale of Conrail, according to Conrail spokesman Saul Resnick. Hagen has said he favors a public stock offering of the government-owned railroad, an option also supported by Conrail Chairman L. Stanley Crane and CSX's Watkins, but opposed by Transportation Secretary Elizabeth Dole.

Hagen, 53, joined Conrail in 1977 as senior vice president for marketing and sales. Hagen's marketing savvy and relaxed manner have earned him wide recognition in the industry.

He was a "driving force behind the regulatory reform" that helped Conrail achieve profitability in 1980, Resnick said.

Hagen, who is said to have designed the strategy to make the new Conrail profitable, was from 1973 to 1976 vice president and then president of the U.S. Railway Association. That agency was mandated by Congress to design a plan for the government-owned railroad.

Hagen's departure is a "big loss," Resnick said. He noted, however, that Hagen had hired many capable people, one of whom is marketing Vice President Charles N. Marshall, his successor in the railroad's top marketing job.

Marshall, a lawyer, joined Conrail in 1978 as general counsel for commerce. After spending several years lobbying for industry deregulation, Marshall was named vice president for marketing in 1983. Earlier, he worked for Southern Railway and the Chessie Systems.

Conrail also named George C. Woodward, assistant vice president for marketing, to replace Marshall. Alfred A. Michaud, currently vice president for sales, was appointed vice president for international sales. G. M. Williams Jr., currently assistant vice president for regional market development, was named to succeed Michaud.