Transportation Secretary-designate Drew Lewis breezed through an amiable two-hour confirmation hearing yesterday by skillfully stroking members of the Senate Commerce Committee and alarming few if any of the many constituencies the department serves.

He called the problems of the automobile industry the single most important issue before his department, although he said President-elect Ronald Reagan has not decided if DOT will continue to be the coordinating federal agency for handling Detroit's difficulties.

He calmed fears in the highway community and said he is committed to mass transit. He promised not to back away from the deregulation of airlines, truckers and railroads, but he agreed that small communities and agricultural areas need to be assured of freight and passenger service. The Coast Guard needs more people and better equipment to do its expanded mission, he said.

In short, it would be difficult to predict from Lewis' testimony any significant shift in executive branch transportation policy, although there will clearly be differing degrees of emphasis from those of the Carter administration.

The hearing room, wall-to-wall with lobbyists from highway, transit, aviation and railroading interests, was full of smiles when Lewis was through. aHowever pleased those people may have been yesterday, however, Lewis told them nothing about the Reagan approach to the Transportation Department budget, saying that will come later, and smiles could change to frowns when that happens.

Lewis has been studying the department from within and reading many reports from various transition task forces, but he also has been spending a good deal of time on policies. It was clear from several exchanges yesterday that he had already met privately with many members of the Commerce Committee and he bantered with them comfortably in public.

For example, Sen. John Danforth (R-Mo.) sought a promise that Lewis would not reverse former secretary Brock Adams' decision to keep the St. Louis airport in Missouri instead of moving it across the Mississippi River to the Illinois suburbs.

"I see no need to change a decision made by Brock Adams," Lewis said. "It was not only a sound economic decision, but with you on this committee, it's a sound political decision."

On the other side of the Capitol, key members of the House Public Works and Transportation Committee were beaming this week because Lewis had called them the day of his nomination to say how much he was looking forward to working with them.

Lewis, a former candidate for governor in Pennsylvania who heads a management consulting firm, made these points among others:

About the future of troubled Chrysler Corp., "I am certain the president-elect would not just stand by and watch something go belly-up if there was a reasonable solution."

The interstate highway construction program, which one transition team has recommended for extinction, "should be defined and completed." Some pieces will never be built for environmental or economic reasons, and should be dropped; then a maintenance effort should be set up to protect the 40,000 miles of interstate freeway already built.

Federal aid to mass transit should be concentrated in capital expenditures and shifted away from operating costs. Immediate elimination of federal operating subsidies, however, "would be virtually impossible without shutting down the bulk of the major mass transit systems."

The setting of speed limits should be returned to the states, although he supported as a safety measure a 55-mile limit for Pennsylvania because of its urban nature. He favors standardized truck weights, particularly on interstate highways, but recognizes the need for states to set their own limits to meet local circumstances.

Some middle ground ought to be found to head off a possible illegal strike by air traffic controllers in March. "I think we approach it not as a strike, but as a negotiation."

Reorganization of Conrail, the financially troubled northeastern freight railway system, should be a priority for the new administration.

The cost benefits of Amtrak are "very questionable" in some areas, but Amtrak appears to make sense in the northeast corridor between Boston and Washington and on such West Coast runs as Los Angeles-San Diego. Then he told the story of the congressman who wanted Amtrak cut, "but not in my district." It is a story congressmen and senators know very well.