President Carter has agreed to four new appointments to the Interstate Commerce Commission, including one candidate whose name was submitted by the Teamsters union, sources said yesterday.

The package of appointments includes:

Marcus Alexis, 46. chairman of the economics department of Northwestern University, Evanston, Ill. Alexis, who has been a professor at Northwestern since 1970, would be the first black member of the ICC in its 92-year history.

Darius W. Gaskins Jr., 41, an economist currently with the Energy Department serving as deputy assistant secretary for policy analysis. Gaskins held the top economics post at both the Civil Aeronautics Board and the Federal Trade Commission before moving to Energy.

Thomas Gray, secretary of the executive cabinet of Kentucky Gov. Julian Carroll. Gray, who served as Kentucky's secretary of transportation for a year, was in private business for 19 years as the owner of an office supply store.

Thomas A. Trantum, a security analyst with Rothschild, Unterberg, Towbin in New York who specializes in regulated transportation. Trantum was virtually the first in the securities industry to support airline deregulation vigorously.

Sources say Gray's nomination is a concession to the International Brotherhood of Teamsters, which is negotiating a nationwide trucking contract the administration considers the key to the success of its anti-inflation program.

Gray was on a list of names the Teamsters told the White House it would find acceptable for membership on the ICC, which regulates interstate truck, rail and bus transporation. Although there is said to have been some disagreement, sources say some White House officials insisted one of the Teamsters' candidates be included in the ICC package.

The names still have to go through Federal Bureau of Investigation and conflict-of-interest checks before they are sent to the Senate for confirmation.

One of the four nominees is scheduled to replace Virginia Mae Brown, whose term expired more than a year ago but who has continued to sit until the White House decided what to do.

Assuming confirmation of all four, the package will boost membership on the ICC to nine, two short of the 11 the law allows. The White House had let the membership decline because 11 was considered unwieldy. Some, including current ICC Chairman A. Daniel O'Neal, had argued that the membership should be no greater than seven.

The nominees are all said to favor reducing federal regulation of surface transporation, fulfilling a promise President Carter made to continue the recent "deregulation" trend at the ICC through his appointments to the agency.

Some administration officials are hoping a reconstituted ICC pursuing competition more vigorously administratively can advance the cause of deregulation as the Civil Aeronautics Board did prior to passage of the Airline Deregulation Act.

At one time, former Rep. Fred B. Rooney (D-Pa.), who was chairman of the House subcommittee on transportation and commerce, was being considered by the White House for a seat on the ICC, but he took himself out of the running.