In between scientific explanations of how construction of a sea-level canal in Central America could threaten marine life, and why an ecologist is needed to study how to head off a swarm of killer bees headed this way from Brazil, Congress got its first accounting yesterday of how much money the Smithsonian Institution gets from private sources and what it does with those trust funds.

Rep. Sidney R. Yates (D-III), chairman of the House Appropriations Interior Subcommittee, halled disclosures by Smithsonian secretary S. Dillan Ripley and his associates -- prodded by a critical investigative report -- that "for the first time allows to Congress to examine the private funds, so we can have a better idea if the Smithsonian needs more or less public funding. Yates said.

This week's hearings also marked the first time that members of the Smithsonian's board of regents had attended a budget session involving the Smithsonian.

In response to a letter from Yates to Chief Justice Warren E. Burger, who serves as chancellor of the 17-member board, James E. Webb, former budget director and head of NASA appeared yesterday in behalf at the regents. Three congressional members of the board also dropped by.

Yates said the appearance and active participation of Webb should result in the regents becoming "where aware of the budget process" and of the ticklish job of balancing public and private obligations of the institution.

As a result of findings in the investigative report, and reforms promised by Ripley. Yates said future meetings of the regents will require "much more formal decision-making." The report said that in the past, regents often were not advised of actions by the Smithsonian staff and rarely took formal votes on issues.

"The Smithsonian is a marvelous institution, and we don't want to cripple it at all," Yates said. But he was anxious to establish a public record of the income and expenditures, both public and private, of "this hybrid federal-private establishment. There is nothing else like it" in the budget-making process.

Now that Congress knows about how the Smithsonian plans to build up a $50 million endowment fund. Yates said legislators "must decide if we should let them move toward that goal, or if we should ease the burden on taxpayers funds" by reducing federal appropriations by a similar amount.

In fiscal 1979, according to Smithsonian treasurer T. Ames Wheeler, $4 million in profits from the popular Smithsonian Magazine and $1.5 million in profits from the institution's various museum shops will be set aside for the endowment.

The goal of the endowment is to form a base to assure income in the future in the event existing trust funds are depleted, or become victims of inflation.