President-elect Reagan yesterday chose the trustee of a bankrupt railroad to supervise the Department of Transportation.

Andrew L. (Drew) Lewis Jr., 49, a short, cheery Pennsylvanian, has broad experience in business and politics. But his only professional link with the transportation industry has been his service over the past 10 years as trustee of the Reading Co., the Philadelphia holding company that used to operate the Reading Railroad.

In 1976, Reading gave up most of its rail operations to Conrail, the federally subsidized freight giant that took over five other failed eastern railroads at the same time. Since then Lewis and a co-trustee have been responsible for reorganizing Reading and managing its real estate holdings.

Lewis in many ways was a natural choice for the trustee's job when Reading went bankrupt in 1971. Prominent in Pennsylvania business and political circles, he has made a career out of reorganizing troubled concerns. He has been called on to revive and redirect corporations in heavy industry (Boston's Simplex Wire) and in the service sector (Philadelphia's Snelling and Snelling, an employment agency chain.)

In the meantime, Lewis also has built up a business of his own, Lewis and Associates of Philadelphia, a consulting firm with particular expertise in aid to struggling businesses. The consulting firm, the trustee's position and Lewis' various corporate directorships have made him a well-to-do man.

Somehow, though, Lewis has found time to take an extremely active role in Republican politics at the state and national levels. His only personal political endeavor -- a campaign for governor of Pennsylvania in 1974 -- was unsuccessful, but Lewis has had considerable success as a party builder, fund raiser and manager of others' campaigns.

In 1976, Lewis was Pennsylvania chairman of Gerald Ford's campaign for the GOP presidental nomination. In that role, he found himself faced with an agonizing choice that pitted a lifetime friendship against his political allegiance to Ford.

As Lewis was working the telephone on July 20, 1976, to make sure that Ford delegates in his state did not switch over to challenger Ronald Reagan, Lewis received word that his lifelong friend and staunch political ally, Sen. Richard Schweiker (R-Pa)., had signed up to be Reagan's running mate. Schweiker called Lewis and asked him, too, to come over to the Reagan side.

Lewis stood firm with Ford. At the GOP convention, most of the Pennsylvania delegation did so, too.

In the 1980 election, Lewis came out early for Reagan, even as most of his allies in the moderate wing of Pennsylvania's Republican Party sided with other GOP hopefuls. He eventually landed in a senior position on the Reagan campaign staff, and has been a tip official of the transition office.

The new transportation secretary, a graduate of Haverford College and Harvard Business School, lives in a 130-acre farm (Lilliput Farms) in Montgomery Country, outside of Philadelphia, with his wife Marilyn, who is a member of the state legislature, and their three children.