The Export-Import Bank opened a campaign yesterday to convince business leaders that Reagan administration budget cuts ending its direct lending program will not hurt the agency's ability to support American exporters.

"At first blush, it appears the Export-Import Bank has lost a major portion of its muscle. But when you analyze it, we haven't lost any muscle," said Ex-Im Bank Chairman William H. Draper III, who spent most of the day meeting with business groups.

Draper's campaign achieved a partial endorsement of the budget cuts imposed on the Ex-Im Bank, as the U.S. Chamber of Commerce's board of directors voted yesterday afternoon to support substantial cuts in the direct loan program -- but not its elimination as the White House wants -- to help trim the federal deficit.

Draper said an alternate program he won from a reluctant Office of Management and Budget would serve as well as direct loans to fight efforts by foreign governments "to steal business from American producers" with subsidized low interest financing.

Under this new program, called "I-Match," the Ex-Im Bank will make up the difference between the subsidized loan and commercial rates, as well as guaranteeing those loans. If a competing foreign government offered subsidized financing to clinch a sale, the Ex-Im Bank would make up the difference between that rate and the higher, market rate.

Draper said the change from direct loans to "I-Match" will save the government $3.4 billion over three years, "and we haven't lost any ability to help exporters to fight foreign government intervention with matching interest rates."

Some exporters were reported as seeing this as "an interesting approach," but were not sure it would work. This led to the Chamber board recommendation that the bank should institute the "I-Match" program on a trial basis while going with a reduced direct loan program.

Earlier Draper meetings on Capitol Hill, however, failed to convince key legislators who traditionally have supported the Ex-Im Bank. Sen. John Heinz (R-Pa.), a ranking member of the Senate Banking Committee, said he is not sure the Ex-Im Bank hasn't lost muscle by killing its direct loan program, especially with Draper predicting a greater demand for its financing.

He is especially concerned because the "I-Match" will provide $1.8 billion in financing compared with $3.865 billion in direct loans available this year.

Draper, though, said that the $1.8 billion will support $3 billion worth of American exports. In addition, he said the bank will be able to provide "hell and high water" guarantees for $12 billion worth of loans -- an increase of $2 billion over 1984.

"We do expect we will be able to do all the financing that is needed, all the demand that will come to us, with the 'I-Match' program and the guarantee program in place," said Draper.

He acknowledged that he had his work cut out persuading Congress and business groups that "I-Match" was an alternative to direct loans. "I got the opinion that they are looking for a monkey wrench in the thing and are nervous about making any changes in what they see as a very successful program," said Draper.

He also sought to assure business groups that they would still be able to get high-risk, long-term financing for big-ticket exports such as jet airplanes and nuclear reactors even without the direct loan program. He said money will be available from a New York banking consortium, the Private Export Financing Corp. (PEFCO), with the Ex-Im Bank guaranteeing the loans.

Draper told a press briefing yesterday that OMB originally wanted to cut the direct loan program without providing any alternative. But he presented "I-Match" as "a good alternative to what he Budget Director David Stockman had proposed" and won the battle within OMB and the White House.

The President's Commission on Industrial Competitiveness, which issued its report yesterday, called for a strengthening of the Ex-Im Bank, but did not address the issue of substituting "I-Match" for direct loans.