The Reagan administration favors speedy passage of legislation allowing the creation of export trading companies, but will oppose proposed appropriations of $20 million a year for the Small Business Administration and to encourage small, medium-sized and minority businesses to export.

In addition, the administration opposes authorization for loan guarantees from the Export-Import Bank to export trading companies or exporters. A large part of the Ex-Im guarantees would promote exports from small, medium-sized and minority businesses or agricultural concerns. The administration opposes the measures as part of its budget-cutting plans, Commerce Secretary Malcolm Baldrige told the Senate Banking, Housing and Urban Affairs international finance subcommittee yesterday.

"As we all strive to reduce government spending substantially, we cannot support new appropriations or authorizations for expenditure programs," Baldrige said.

The administration also is against the proposed establishment of a special office of export trade to carry out some of the functions of certifying and promoting the trading companies because Commerce Department offices already can do that, Baldrige said.

The legislation passed the Senate by a 77-to-0 vote last year, but never made it through the House. It would authorize commercial banks to have an interest in export trading companies and would exempt them from appropriate antitrust laws. The purpose of the trading companies is to promote exporting in the fashion used sucessfully by the Japanese and the Europeans for decades.

The trading companies, using economies of scale, would market efficiently American goods, particularly of small- and medium-sized firms that can't afford to export by themselves. More exports could help reduce the country's trade deficit, strengthen the dollar and lead to more employment here, proponents contend.

Sen. John C. Danforth (R-Mo.) testified that the legislation has been kicked around Capitol Hill for more than two years. "Even Gargantua didn't have such a long gestation," Danforth said. "As painful as it is, birth has to come. The baby has to be delivered."

The bill's opponents have argued that the proposal would seriously breach the separation of banking from commercial affairs which is intended to preserve banks' soundness and impartiality in providing credit. The legislation also could give large banks, new monopoly powers while supposedly helping small businesses, opponents contend.

Federal Reserve Board Governor Henry Wallich testified that bank control of export trading companies would increase the potential financial risks to the banks.