Rep. Michael Barnes, a U.S. Senate candidate with a critical need to win support beyond his Montgomery County base, today brought some Capitol Hill clout to bear on a major concern of the state's biggest city and voting bloc.

With his lead witness Baltimore Mayor William Donald Schaefer, himself a likely candidate for statewide office, Barnes held a three-hour hearing on "The Role of Western Hemisphere Trade and the Port of Baltimore." The hearing was designed, according to the announcement, to "identify specific steps to increase cargo levels in 1986," specifically through expanded trade with Latin America, an area in which Barnes specializes as chairman of a House Foreign Affairs subcommittee.

But it also brought together a few of the leading actors in the economy of the city, and therefore of the state, at a time when both the port and Barnes, whose Senate bid trails in early polls behind that of Baltimore's popular Rep. Barbara Mikulski, could use the exposure.

Barnes noted that the port has continued to lose business and income to competition from the Virginia ports at Hampton Roads during the last two years, with general cargo down 17.8 percent from the previous year.

"We need to initiate an aggressive effort to seek out new business," he said. " . . . I am convinced that we could start this effort by looking here in our hemisphere, by looking toward Latin America . . . . As one who has visited our major trading partners in South America -- Argentina, Brazil, Chile, and Venezuela -- I can personally attest to the vitality and energy of their economies."

Barnes then turned the microphone over to Schaefer, whom he hailed as "the best mayor in America." Schaefer, an all-but-announced candidate for governor who is also working to broaden his statewide appeal, thanked Barnes for holding the hearing and focusing attention on the port, which he called "vital to the whole state."

Schaefer emphasized his support for a long-delayed, federal-state project to deepen the harbor's main channel for bigger ships.

Asked later whether his appearance at the meeting indicated a budding support for Barnes' candidacy, Schaefer laughed and said he came because, "I was invited by Congressman Mike Barnes. This isn't the first time I've been down here; I've been down here 10 times to promote the port. Anytime you do anything people want to question your motives."

Asked whether he viewed Barnes' hearing as an attempt to woo the Baltimore constituency, Schaefer said, "I don't interpret any move by any congressman to do anything for the state of Maryland as being all political or part political. Nothing but good can come out of this."

Equally low key was a Mikulski representative. Said campaign manager Wendy Sherman, "I think we are glad that Congressman Barnes has come to appreciate the importance of the Port of Baltimore to the city and to the states' economy. These are issues that congresswoman has worked very hard on." Sherman mentioned Mikulski's early and consistent support for harbor dredging and efforts to obtain funding to help the port upgrade its facilities.