Reagan administration plans to eliminate export credit subsidies ran into stiff opposition yesterday, as business interests and senators of both parties accused the White House of ignoring the trade deficit in its effort to trim the budget deficit.

"In effect, the Office of Management and Budget has turned a blind eye to our trade problems and has pulled the rug out from under American exporters," said Sen. John Heinz (R-Pa.), who held a Senate Banking Committee hearing on the Export-Import Bank of the United States.

Noting that last year's trade deficit hit a record $123.3 billion, Heinz added that eliminating direct loans for the Ex-Im Bank would hurt efforts to improve the trade balance and force American companies to shift manufacturing plants offshore to sell overseas.

Dean Thorton, senior vice president of Boeing Co., one of the prime beneficiaries of Ex-Im Bank loans, said cutting $3.83 billion in direct loans to finance overseas sales will hurt the trade deficit "significantly" without providing much help in cutting the budget deficit.

Sen. Christopher Dodd (D-Conn.), moreover, suggested the administration's "start-and-stop philosophy" with the Ex-Im Bank -- consigning it to the budgetary ash heap in 1981, resurrecting it temporarily in Reagan's 1983 State of the Union Address, and then eliminating a major program in the current budget -- hurts American exporters.

But administration officials, headed by Ex-Im Bank Chairman William H. Draper III, defended eliminating the bank's direct-loan program, and said a new program for matching subsidized foreign competition will fill in the gap. Under this program, Draper said, the Ex-Im Bank would make up the difference between commercial lending rates and lower, subsidized rates offered by other countries to sell their products.

He also denied the administration "is in a start-stop" mode with the Ex-Im Bank, insisting that the new program to "buy down" interest rates would take the place of the direct-loan program.

The bank also would get an increase of between $10 billion and $12 billion in its guarantee and insurance program.

Business witnesses took a less optimistic view. Ending the direct-loan program, said Donald McGraw of Kellog Rust Inc., "will close the door on future exports of material, equipment and services from the United States." Wayne Moore of Moore Special Tool Co. Inc. of Bridgeport, Conn., called eliminating direct loans "a symbolic move" that sends "signals to other countries that we are going to be less competitive."