The Reagan administration is drawing up plans to establish a Federal Credit Agency within the Treasury Department, perhaps as early as next year, to try to collect more of the government's delinquent loans.

Since it took office, the administration has tried to reduce the government's portfolio of delinquent loans. But the new proposal would for the first time centralize efforts to collect the debts, according to Joseph R. Wright, deputy director of the Office of Management and Budget.

"There's gold in them thar hills," Wright said, pointing out that the government is able to collect only about 15 to 20 percent of overdue loans, compared with the 80 to 85 percent that the private sector collects.

OMB officials said they believe that they can establish the agency within Treasury without seeking approval by Congress. However, one official said the plan might encounter "some problems at the agencies that think they are doing a good job managing their accounts."

Initially, the new agency would be given the task of collecting the Small Business Administration's delinquent loans. If the administration succeeds in getting Congress to abolish the SBA, the new agency would take over the SBA's entire $16 billion loan portfolio.

In that case, Wright said, the new agency would start to sell off to other lenders the SBA's good direct loans and manage the loans that remain with the government.

Robert Turnbull, SBA's associate deputy administrator for management and administration, said, "Over the past three years, our collections have increased by 25 percent. We have put a great deal of emphasis on the collection of delinquent loans."

But, he said, "private-sector institutions tend to be more aggressive than we are. They would go further . . . . If a debt is owed, we should collect it."

In fiscal 1987, the credit agency would grow, adding the Agriculture Department's delinquent farm loans, the Education Department's delinquent student loans, the Veterans Administration's delinquent home-mortgage loans and delinquent loans made by the Commerce Department's Economic Development Administration. The agencies, however, would continue deciding who qualifies for a loan, according to OMB officials.

According to Wright, OMB staffers are working with Carole J. Dineen, assistant secretary of the treasury for fiscal affairs, on the proposal for the new agency. Neither Dineen nor her senior aides would comment on the plan.

OMB estimates that about 20 percent of loans made by the government are overdue or in default. Agency officials said the amount totals $23 billion; in 1982, the figure was put at $38.4 billion.

"It is essential that the federal government realize the importance of good management of loan portfolios," Wright said.

The Grace Commission on improving federal efficiency also recommended that the government improve its loan-collection efforts. It said that collection records should be computerized, but stopped short of recommending that efforts be consolidated in one agency.

In summary of its findings, the commission said, "The government's loan programs perform poorly for several reasons. First, loan quality is not the foremost concern in the public sector. Indeed, many federal lending programs establish as a prerequisite the denial of credit by a private-sector lender. Second, once the government's loan officers make a loan, its repayment is not nearly as important to them as it would be to a private-sector lender."

Wright, a former vice president for credit marketing at Citicorp, said his former firm and others usually refer overdue loans to a collection agency if the firm's own methods have failed and the account is at least six months overdue.

"In the . . . government, we are operating almost in the exact opposite fashion," he said. "We don't even try to start collecting until an account is six months old, it seems."

At that point, according to OMB statistics, most agencies make between three and six attempts to collect a delinquent loan before declaring that the borrower has defaulted. In the private sector, he said, 30 attempts probably would be made.

Over the past few years, OMB also has worked with Congress to enact legislation to strengthen agency collection procedures and to require agencies to begin reporting the credit records of federal borrowers through the Dun & Bradstreet network of credit bureaus.

"For the first time, a federal loan officer or a bank loan officer has an applicant's federal and private-sector credit experience available in a single report," an OMB report on that program said. "Federal agencies will not be allowed to make a loan, loan guarantee, contract or grant without coordinating with another federal agency with adverse experience, if it exists."

Although the Debt Collection Act of 1982 required 20 major lending agencies to issue regulations to improve their credit-collection procedures, OMB favors a centralized system.

"We have to bring in some top-notch credit management staff and use the automated systems at the IRS to do this," Wright said. "It's not as simple as writing a letter."