Opponents of a bill that would curb court-ordered busing for school desgregation lost two test votes yesterday in the Senate Judiciary Committee.

However, no final action was taken on the measure because a quorum was lost while Sen. James Abourezk (D-S.D.) was reading a letter from Attorney General Griffin B. Bell opposing the bill.

Sen. James O. Eastland(D-Miss.), chairman of the committee, immediately scheduled another session for this morning.

Bell's letter Eastland had been furnished to all the committee members, but Abourezk insisted on reading it in full. He and other opponents have been trying to stall action on the bill, which appears to have majority support within the committee.

Under the bill, a federal judge would have to determine that a discriminatory purpose in education was a principal motivating factor in the racial segregation of a school before he could order busing as a remedy.

Sen. Howard Metzenbaum (D-Ohio) offered an amendment to strike the word "principal." He cited Bell's letter saying this language "would unnecessarily complicate the process of proof in school desegregation cases."

However, the amendment was tabled by a 7-to-4 vote after Sen. Joseph Biden (D-Del.), a principal sponsor of the bill and others urged its rejection.

Biden said the word principal or something like it should be in the bill so that racial discrimination by school officials would have to be more than just ond of several factors involved.