Some federal agencies next week will begin to lift or modify the solid hiring freeze President Reagan slapped on the bureaucracy the day he took office (Jan. 20) and later made retroactive on Nov. 5, the day after he was elected president.

Decisions will be made on an agency-by-agency basis beginning March 10, when they will get first official word of new personnel-budget ceilings Reagan will propose for them.Although some agencies have unofficial word on new, lower ceilings, the official "allowance letters" from the Office of Management and Budget will not be mailed out until midweek. When agencies get the official word they can begin deciding if they are over or under new ceilings and whether they can resume hiring or must keep the freeze on until they slim down further.

The government hires about 1,500 people each workday, mostly to replace persons who resign, retire or die. Hiring has been cut sharply since Jan. 20, except for political slots and emergency-type jobs. Department of Defense has been the exception. It lifted the civilian hiring freeze last month when it became clear that Army, Navy, and Air Force would get more jobs in the coming Reagan budget while most nondefense operations will get fewer people than Carter proposed for them for September 1981 and September 1982.

It will take about a week for OMB to get the allowance letters out to each agency. Then it will take more time for agencies to see if they can hire, or must stick with the freeze.

Thousands of people promised jobs between Nov. 5 and Jan. 20 were caught by Reagan's retroactive freeze order. Only a handful have been hired for "hardship" reasons. (The retroactive freeze was upheld Feb. 25 by U.S. District Court Judge Charles R. Richey. The National Treasury Employees Union, which challenged the legality and constitutionality of the back-dated freeze order, is appealing to a higher court.)

If you are job-hunting, or were caught by the freeze, don't expect instant success next week. Agencies will be notified of their new job-dollar status beginning March 10. It could be several more weeks before agencies know what their hiring status will be.