Clarence M. Pendleton Jr. has turned his part-time post as chairman of the U.S. Commission on Civil Rights into a nearly full-time job that paid him $67,344 last year, although that amounts to less than half his income from outside ventures.

That is among the findings in an unreleased General Accounting Office report that found widespread mismanagement at the commission. The report, to be made public at a House hearing today, also said that political groups, oil companies, television networks and other sources improperly paid for some of Pendleton's travel.

The GAO findings come amid a Small Business Administration investigation of Pendleton and his special assistant, Sydney I. Novell, who earned $41,328 at the commission last year. While serving as chairman of a federally funded San Diego firm that packages SBA loan applications, Pendleton arranged a noncompetitive contract for Novell that pays her $60,000 a year plus commissions, according to Media General News Service, which disclosed the SBA probe.

Pendleton, who is also a partner with Novell in a consulting firm, said he resigned as chairman of the San Diego County Local Development Corp. in January.

An outspoken black conservative who lives in San Diego, Pendleton dismissed the GAO probe as "politically motivated." He said his salary and expenses were higher than his colleagues' because "the chairman has a lot of responsibility . . . . The taxpayers are more than getting their money's worth."

Pendleton referred questions about the SBA probe to his San Diego lawyer, who could not be reached yesterday.

The GAO report said Pendleton received $188,000 in salary from the commission for 233, 233 and 240 days of work over the last three years, more than twice the number of days charged by any other commissioner. Novell charged for 239 days last year. A full-time work year is 260 days.

Pendleton also outpaced the other commissioners by charging the government $29,300 for 36 trips last year. In the last four years, the GAO said, outside groups have paid for Pendleton's travel or lodging on 45 of 117 trips.

The auditors said Pendleton did not identify most of these groups on his vouchers and that it is a violation of federal rules for him to accept gifts from for-profit companies.

Pendleton, former head of the San Diego Urban League, remains involved in numerous private ventures. Among his other ventures in 1983, according to his financial disclosure statement, he received $23,500 in director's fees from Great American First Savings Bank in San Diego; $700 in director's fees from San Diego Transit Corp. and $4,200 in fees from two other groups.

In the last nine months of 1982, while serving as commission chairman, Pendleton also was paid $42,500 as president of the New Coalition for Economic and Social Change.

Commission staff director J. Al Latham Jr. said agency lawyers had decided that it was "perfectly lawful and proper" for officials to accept travel expenses from outside groups because they have no regulatory powers. He said the GAO denied his agency "due process" by not including its comments in the final report.

The GAO review, requested by Reps. Don Edwards (D-Calif.), Patricia Schroeder (D-Colo.), Augustus F. Hawkins (D-Calif.) and Matthew G. Martinez (D-Calif.), found that:

* The commission has hired a large number of political appointees, consultants and temporary employes, instead of career federal workers. In one 27-month period, the commission made 212 such appointments while hiring 60 career employes.

* There were irregularities in the hiring of all 31 consultants and 23 temporary employes examined by the GAO. Consultants were improperly allowed to manage commission projects and supervise career staff, while some temporary employes were hired after the application period had closed.

* Three political appointees were directly promoted from GS-7 jobs to GS-11 and GS-12 positions, and a fourth received a $30,000 salary increase in 17 months.

Latham said the commission has hired "a very distinguished group of consultants" and that there is no evidence that rules were broken or career employes shortchanged. "All these areas are narrow, technical questions that do not involve any claim of malfeasance or misappropriation of funds," he said.