If the town seems a little less crowded since Ronald Reagan rode in, it is because the U.S. government here has shrunk to 346,282 people--a drop of 20,421 between February of 1981 and February of this year.

Outside of Washington, Office of Personnel Management head counters say, the federal work force is down 30,425, even though Defense Department agencies--Army, Navy and Air Force--hired an additional 40,816 people.

Despite all the talk of RIFs, actual layoffs for economy reasons in metropolitan Washington have totaled about 1,900 in the 12-month period. Most job cuts reflect attrition as agencies imposed hiring freezes or slowdowns in hiring under orders to meet new, lower personnel ceilings.

Biggest drop in employment has come at Health and Human Services (which with Congress and the Navy ranks among the top three government employers here) which lost 9,700 jobs nationwide; Transportation (11,400 air traffic controllers fired) with a total decrease of 10,293 jobs; Commerce because the census was completed; Agriculture, which dropped 7,500 jobs and Interior, which reduced employment by just over 6,000 positions.

Defense hired a large number of civilians during the period; Army added 17,500 new jobs; Navy, 11,400 and Air Force just over 10,600. The U.S. Postal Service, a semi-independent corporation, increased its work force about 6,000 during the period, according to the OPM data.

OPM said the total number of federal workers--executive, legislative and judicial branches--was 2,852,658 as of last February. It said the monthly federal payroll was $5.3 billion, and that the February payout here was $752 million. The figures for the metro Washington area do not include workers at the Central Intelligence Agency, the National Security Agency (both of which have had buildups) nor the District of Columbia government.