Spokesmen for military associations said, yesterday that the armed forces and civilian government could lose many of their best people if Congress cuts off retired pay now going to 141,000 ex-military personnel holding civil service jobs.

Representatives of various service organizations told the Hous investigations subcommittee that the retirees are victims of "guerillas warfare" attacks from hostile segments of Congress, the press and the public.

The subcommittee is preparing to write legislation to end or reduce the practice of double-dipping that permits most of the retirees to draw full pension and civilian salary while working for Uncle Sam.

Approximately five of every 100 federal employees is a military retiree eligible for both military pension and civil pay. Congressional estimates range up to $1 billion a year as the value of the pensions received by those retirees who ranged from sergeants holding low-level government jobs to retired admirals and generals who make more than Vice President Mondale or the chief of staff.

The groups testifying in opposition to any sudden drastic changes in the dual compensation law included the Retired Officers Association, Air Force Sergeants Association, National Association of Uniformed Services (NAUS), Non-Commissioned Officers Association, Fleet Reserve Association and Veterans of Foreign Wars.

Although the groups often fight over "turf" and sometimes disagree on legislative proposals, they were united yesterday in asking the no changes be made until a comprehensive study of all federal retirement systems is completed by a White House panel. Retired Air Force Gen. Benjami O. Davis, who is heading that study, was in the subcommittee meeting room yesterday.

John Sheffy of NAUS did much of the talking for the combined groups. He warned the panel that a cutback in the dual compensation laws would constitute a gross "breach of contract" betweent the government and its active and retired military personnel. Sheffy predicted a cutback in dual compensation would hurt military recruiting and force many of the retirees in government to leave to take other jobs in which they could keep their pensions.

Most of the military group spokesmen agreed that the core of the problem is the forced early retirment system in the military, which pushes people not bound for general or admiral jobs out after 20 years.

Sheffy, who predicted a military retiree exodus from government, said these "valuable military people are not going to work for the government" if they are forced to give up retirement pay. He gave the example of a retired master sergeant getting $5,000 in pension while in government , Sheffy said, " he could go to work in a filling station for $8,000 a year and be better off."

Military retirees in government believe their special position and problems have rarely been presented to the public in a fair manner. Most say that they cannot support families on a military pension, and that it is only natural for military retirees - who make up 5 per cent of the total civil service work force - to look to government where they have job contacts, and where their skill are most in demand.

Donald H. Schwab of the VFW said too much attention has been paid to the "handful" of retired admirals and generals who each draw more than $80,000 in retired and civilian pay. The facts are, Schwab told subcommittee chairman Robert N. C. Nix (D-Pa.), that 80 per cent of the military retirees in government are former enlisted personnel whose pensions are the established poverty level for a familty of four.

Schwab said that 22,000 retired reserve officer - who can keep full pension and pay - get an average of $8,000 a year in retired pay. Most have to work at other jobs, he said, and most of them are forced to retire from the military after they failed to get promotions.

Reserve Officer's Association's John Wanamaker said the typical military officer today is "forced out" after 26 years of service, at age 46 with a pension of $14,750. He said military pensions are, in fact, an "earned form of deferred pay" and shouldn't be taken away.

Most of the witnesses said they would welcome name, location and salaries of the off-cited admirals and generals who make more than anybod in government except the President. And they said they oppose buddy-system hiring one of the things that makes civilian federal workers bitter about the presence of retired military people in their offices.

But the military group spokesmen urged the subcommittee and Congress not to act quickly to eliminate the double-dipper benefit until the entire question of costs, equity and feasiblity has been studied.