The National Association of Counties has joined Prince George's County in opposing measures sponsored by Sen. Alan Cranston (D-Calif.) that would limit the height of the proposed 52-story PortAmerica tower near Oxon Hill to 14 stories.

At its annual convention in Las Vegas this week, the association approved a resolution sponsored by Prince George's delegates labeling the Senate bills as an "unacceptable federal intervention" in local land use.

The proposed federal legislation would limit the height of all buildings in the close-in Washington suburbs to 14 stories, and would require a developer who wished to exceed the limit to pay $1 million for each foot above it.

The proposed tower, the centerpiece of the $1 billion office, retail and residential complex to be built by developer James T. Lewis south of the Woodrow Wilson Bridge, was given final approval along with the rest of the PortAmerica complex by the Prince George's County Council this month.

* Student Loan Authority Members Named County Executive Parris Glendening has nominated five persons to serve on the county's newly created Higher Educational Loan Authority, which will provide up to $35 million worth of low-interest student loans to middle-income county residents.

They are retired Air Force Col. James Snight of Clinton; Manervia Riddick of Fort Washington, vice president and operations manager of MetroVision Cable Co.; and Clarence Godfrey of Mitchellville, a computer scientist at the David Taylor Naval Ship and Development Center in Bethesda. Also, JoAnne Goldsmith of District Heights, a vice president of John Hanson Savings and Loan; and Jean Spencer of Greenbelt, former executive director and chairman of the board of trustees of Maryland State Universities and Colleges.