Office of Management and Budget officials are working on detailed instructions, due out in a couple of days, that will tell government agencies how to handle the "strict freeze on hiring" President Reagan ordered moments after he took office. Until those instructions are out, OMB brass say, nobody is to be hired in the executive branch, for any reason. Period!

Ordering a freeze is easy. Implementing and interpreting it is not easy. OMB officials are now deciding what kinds of jobs will be exempt from the no-hiring order, and what to do about people who have been promised jobs. That question is still up in the air.

This is the problem: Despite a partial hiring freeze last March by President Carter, some agencies in recent months have fattened their payrolls and sent out job promises to people, hoping to beat the Reagan freeze. A report here Jan. 14 that Reagan had ordered OMB to draft the freeze message (the one issued Jan. 20) spurred many agencies to send out commitment letters, according to OMB brass.

Reagan aides and career officials at the OMB are furious about the last-minute hiring by agencies. They repeatedly cite the Department of Education as one of the worst offenders. At the moment OMB officials and Reagan aides are of two minds about the implementation of the freeze: One group wants to make it effective Jan. 20. But there is strong sentiment, as reported here Tuesday, to make the freeze retroactive to Dec. 31. That would mean nobody who got a job after that date can be hired.

"Some federal agencies have abused the thing, and put out commitments contrary to Carter regulations and those anticipated from President Reagan," an OMB official said yesterday. He said it is "very possible" that the hard-liners will win out, and that the Dec. 31 cutoff date will be included in the upcoming freeze implementation regulations.

Right now that issue is undecided, along with the question of what jobs will be exempt from the freeze -- including thousands of political and Schedule C slots available to the administration. OMB will supply the answers within the next couple of days. In the meantime, as one top official said, "I wish you would get out the word -- no hiring until further notice. None at all."

For unbelievers, here is a partial text of Reagan's Jan. 20 memo to heads of executive branch departments and agencies:

"I am ordering today a strict freeze on the hiring o federal civilian employes to be applied across the board in the executive branch.

". . . The director of the Office of Management and Budget will issue detailed instructions concerning this freeze. I am delegating to him authority to grant exemptions in those rare and unusual circumstances where exemptions are necessary for the delivery of essential services."

Reagan said that agencies should make sure that offices dealing with Social Security claims, payment of veterans and retirement benefits are staffed, even if it means shifting people from other, less essential work. "Obviously," his memo said," contracting with firms and institutions outside the government to circumvent the intent of this directive must not be permitted."

Lots of calls yesterday from federal workers who are planning to shift to jobs in other agencies. They want to know if the freeze will affect them. That is one of the big questions to be answered in the OMB directive coming up.