Thousands of government employes can expect to receive a stern warning from their bosses over the next few weeks: repay their federally guaranteed college loans or the government will begin withholding up to 15 percent of their paychecks until the debt is settled.

The move is part of a broader campaign by the Reagan administration to recoup more than $2 billion in delinquent student loans and $23 billion in other government loans that are overdue.

Besides ordering federal employes to pay up, the government also has:

* Turned over the names of thousands of delinquent debtors to national credit rating services, in hopes of lowering their credit ratings.

* Hired two private national collection agencies, known in some agencies as "bounty hunters," to track down borrowers.

* Begun penalizing states and universities having student loan delinquency rates that are higher than average.

* Backed legislation now before Congress that would permit federal agencies to hire private attorneys to litigate collection suits. Agencies have complained that U.S. attorneys have displayed little enthusiasm for pursuing small-scale debtors.

Just how many federal employes will receive warning letters over the next three weeks is unclear. Education Department officials distributed sealed envelopes containing the names of 41,000 delinquent borrowers to agencies on Wednesday, but some of those names were culled from government personnel records that were two years old.

Agencies were asked to compare the Education Department lists with their current personnel records to identify which debtors still work for the government.

Richard Hastings, director of the Education Department's office of student financial assistance, said he believed that at least two-thirds of the persons on the master list still work for the government.

The department compiled its list, he said, by using a computer to match lists of delinquent debtors with federal personnel records that contained the names of 10.3 million government employes, including National Guard troops, retired civil servants and postal workers. The match found 46,860 names on both lists. They accounted for more than 50,000 loans valued at $67.7 million.

Hastings said the department sent letters demanding payment to those employes and recovered $3.4 million from 8,417 persons who made full or partial payments.

Hastings said the agencies will tell employes that they have 15 days either to repay their loans or to contact the Education Department to arrange a payment schedule. If the department does not hear from a debtor by Nov. 15 it will ask the agency to withhold a portion of the employe's wages.

Most of the delinquencies are in the Guaranteed Student Loan Program, involving loans of up to $12,500 from local banks. The loan is due six months after graduation. If the borrower defaults, his state pays the bank and then seeks repayment from the federal government.

The other program, the National Direct Student Loan Program, is smaller, but its collection rate is worse. It is administered by colleges, which put up 10 percent of the principal to the government's 90 percent. Students who demonstrate need can borrow up to $6,000 over four years at 5 percent interest.

Last year, as part of the Debt Collection Act of 1982, Congress for the first time authorized federal agencies to garnishee their employes' wages.

The law was passed after numerous hearings by a Senate Governmental Affairs subcommittee chaired by Sen. Charles H. Percy (R-Ill.). At one hearing, Percy said the Education Department had hired an attorney two years after he defaulted on a $4,000 student loan.

The employe refused to repay the loan until the government sued him. He eventually repaid the debt last year after he had been promoted twice, Percy said. A Percy aide refused to identify the employe, and the department would not release any of the names it distributed to agencies.

Hastings said White House employes were included on the personnel lists that the Education Department checked but no defaulters were turned up. The names of congressional employes, however, were not reviewed.

Last month, Stanley M. Brand, general counsel for the Office of the Clerk of the House, declined a U.S. attorney's request that a congressional employe's wages be withheld because he was in default on a government loan. Brand said that in his opinion the law, as drafted, did not apply to the legislative branch.

Hastings said he knew of some congressional employes who have defaulted on student loans but didn't know how many.