Friday will be the last workday for many government employees who are retiring -- some much earlier than they originally intended -- to take advantage of a popular pension perk that will disappear Dec. 1.

Longtime civil servants, who came into government when Dwight D. Eisenhower, John F. Kennedy or Lyndon B. Johnson were in the White House, will be making final rounds at the office or will be roasted and toasted at special luncheons by contemporaries and new associates, some of whom weren't even born when the guests of honor got their first jobs.

The reason for the retirement rush is the end of the popular lump-sum pension benefit option. Seven of every 10 federal retirees has taken it since it was first offered several years ago.

Congress and the White House decided to eliminate the option as part of the deficit-reduction plan approved last month. Congress gave federal employees until the end of this month to retire and qualify for the benefit.

Retirees who elect to take reduced annuities can get a two-stage lump-sum pension payment. Pensions are reduced from 5 percent to more than 25 percent, depending on age and service time of the retiree.

The lump-sum payments, which are taxable, equal the amount of money that the retiree contributed to the civil service retirement system -- about 7 percent of total federal salary -- while working. The payout is split 50-50. The first check arrives shortly after retirement; the second is supposed to arrive one year after the first payment.

Although the lump-sum payments technically are being suspended (as opposed to eliminated) only for five years, insiders doubt they will be restored.

After Dec. 1, the only people who will get the lump-sum option will be those taking regular (not disability) retirement because of a terminal illness, those whose jobs are being abolished or transferred outside the normal commuting area, and Defense Department civilians who are eligible to retire now but who were asked to stay on because of Operation Desert Shield. Homeless Veterans

The Department of Veterans Affairs Employee Association will hold a Dec. 5 concert at Constitution Hall to raise money for homeless vets. Tickets are tax deductible, and the money will be used to help feed, clothe and entertain the needy during the Hanukah and Christmas seasons. For details or tickets, call the VA Medical Center 202-745-8517. People

John Ablard has received the Navy's top civilian honor, the Meritorious Service Award, for his leadership of the Naval Research Laboratory's contracting division.

Samuel L. "Billy" Middleton is retiring this week after 27 years of walking one of the nation's most unusual police beats, the National Zoo. He joined the police unit as a private. He became police chief in 1976 and then head of the safety and police office.

Charles Holland is retiring Friday after 48 years of federal service, all but six of them as a diplomatic security specialist with the State Department.