A General Accounting office audit of three House committees has found 11 instances where subcommittees employees in December, 1975, were paid year-end bonuses - one of them for $2,000.

House Administration Committee Chairman Rep. Frank Thompson Jr., (D-N.J.), who commissioned the audit done last year, reviewed the findings last October and decided against auditing any other committees because of lack of results and cost, about $6,000 each, according to an aide.

The year-end bonuses were the only major finding of the audits of three committees and their subcommittees. Capitol Hill sources said yesterday the bonus practice is followed in many committee and members' offices.

"The Christmas bonus system for Hill employees is more widespread than I would like to see," one veteran House aide said yesterday.

Rep. William Ford (D-Mich.), chairman of one audited subcomittee that paid three bonuses, defended the practice as "extra compensation for having saved money all year long."

William Cable, chief clerk for the House Administration Committee, said yesterday the bonuses are "not improper under House rules" and often were "a reward for frugality to staffers who must live on tight budgets the rest of the year."

Curtis Prins, staff director of a House Banking subcommittee that paid six employees bonuses in December, 1975, said GAO auditors told him the practice was "questionable."

Cable said the GAO characterization of "questionable" meant "not allowable under the Civil Service (payroll) system" and was not a judgement on the House practice.

Ford's Agricultural Labor Subcommitee staff workers received bonuses of $1,000, $500 and $450 in December 1975, according to the GAO. The bonuses were paid in the form of salary increases for each for December only.

The next month, according to the GAO auditors, the salaries "were decreased by the same amount."

Sord said he has followed the practice of giving year-end bonuses all four years he has headed the subcommittee of the Education and Labor Committee.

"My people are not paid the maximum possible," he said, "to be certain there is enough money for the subcommittee's travel and other expenses."

Each December, Ford explained, he looks at the subcommittee budget and determines from the funds left over what bonuses can be paid.

"I get the maximum out of the resources given us," he said, adding that if the bonus system is eliminated he would raise the annual salaries of his full-time subcommittee employees.

The Equal Opportunities Subcommittee of Education and Labor was also found by GAO to have given two December bonuses.

One part-time employee, who received $400 a month for nine months of 1975, got $2,400 in December of that year, according to the GAO. The next month, the first month of a new year and new budget, that employee's pay was cut back to $300 a month.

Another part-time employee, who was making $833 a month, received an additional $1,500 in November and December, 1975.

Susan Grayson, who was on the staff of the subcommittee at the time, said that "the money was paid in a lump sum in lieu of an annual raise."

She said the subcommittee followed that practice because it did not know how much money would be available from one year to the next. When there were funds in December, she said they were paid out.

The Banking subcommittee gave December bonuses to six employees in amounts ranging from $100 to $350, according to GAO working papers. Together they totaled $1,290.

Staff director Prins said the bonuses were given along with pay raises in December "These people were entitled to raises," Prins said, "and it was done this way . . . to give them money at Christmas time."

Prins said he checked in 1975 with the House Administration Committee and was told "it is permissible."