Congress has two federal employe-related items on its agenda (not very high on the agenda) when it returns next week.

It will consider the 3.5 percent pay raise President Reagan has proposed, and probably raise it to 4 percent. Although some House Democrats will try to get the raise made effective next month, odds are it will not come until January.

Congress also must decide what to do about the federal employe health-benefits program. It covers 10 million people, including many members of Congress. Health insurance coverage is the one area where government workers are definitely behind the private sector.

Benefits will be cut next year. Premiums will go up. Most people think something has got to give. This is what is being considered:

* The administration wants to give federal workers and retirees a voucher (check) at the beginning of each year to purchase health insurance. If the premiums were less than the amount of the voucher, workers could keep the difference. If they chose a more expensive plan, they would have to pay the difference in premiums out of pocket.

* Rep. Mary Rose Oakar (D-Ohio) and Sen. Ted Stevens (R-Alaska) want the government to pick up a bigger share of the total premium. The government now pays from 40 percent to 75 percent of premium depending on the plan a worker picks.

* Some House Republicans will offer a proposal that would let the government pay all the premium if an employe chose a plan whose premium was less than the average premium charged by the six largest plans in the program.