If President Reagan gets his way in raising the age for a full federal pension from 55 to 65, Herbert Green said yesterday, "it's going to mess up my life's plan."

The proposal also would have far more serious consequences, according to the 44-year-old federal worker: it would force thousands of older employes to stay on the job much longer than they had planned and prevent a much-needed infusion of "younger blood" into federal agencies.

"I have worked for government 21 years, and if I have to work another 21 before I retire, I don't think I'll be worth as much to the government," said Green. "I think it's important we give younger people a chance, or we will reach the point where we have old guys sitting here and the younger generation will not be prepared."

Green, who earns $41,000 as deputy chief of program review for the Department of Labor's Job Corps, is among the many career federal employes who are upset and angered by Reagan's proposed 1986 budget, which includes the deepest cuts in pay and benefits for federal workers since the Great Depression.

While Green believes Reagan's changes would force people like him to stay longer to get full pensions, other critics say that some aspects of the proposal -- a 5 percent pay cut next January, a reduction of 35,000 jobs and reduced cost-of-living adjustments for pensions -- will induce many workers to quit sooner.

"The very life of the civil service system is threatened by this policy of punitive cuts," said Rep. Mary Rose Oakar (D-0hio), a senior member of the House Post Office and Civil Service Committee. Federal employe unions also denounced the proposed cuts as unfair and unjustified, and predicted the largest exodus of federal workers ever and a deterioration in government services.

Robert Tobias, head of the National Treasury Employees Union, called the plans "a design for national tragedy" because bright, young students are already shunning government service and will be more discouraged by cuts.

A bipartisan chorus of opponents predicted defeat for many elements of the proposal, which congressional critics and federal employe unions have labeled the worst budget in history for federal workers. Rep. Frank Wolf (R-Va.) declared the pay cut proposal dead-on-arrival.

The Office of Personnel Management contends that virtually all the proposed changes in benefits are in line with the current practice of private employers and should not prompt defections. The cuts, according to the administration's budget message, are designed to reduce what the public regards as an "expensive, overly generous retirement system" that exceeds most private-sector benefits.

Green, who started his government career in 1963 as a passport clerk at the State Department, has worked for the Postal Service, D.C. General Hospital and, after obtaining a master's degree in public administration, the Consumer Product Safety Commission and the Labor Department.

After working in five agencies, Green said he believes one of the most serious problems is the "entrenched" workers who become narrow in their thinking -- and lazy.

While the president has said he wants the bureaucracy to become more responsive, the retirement cuts would have the opposite effect, Green said, because "you are going to have guys close to 70 years old sitting here and waiting to leave."

Early retirees would be penalized 5 percent per year below age 65 under the proposal. For example, retirement at 55 would trigger a 50 percent reduction, which Green said many federal workers could not afford. Pensions are about 55 percent of base pay, although the budget also contains a new formula that would slightly reduce that level.

Green said he was "particularly disillusioned" because the budget would eliminate his program, the Job Corps, the $600 million yearly training effort for disadvantaged youths. The administration believes the program is not cost-effective, but Green said some clients, deprived of training, will end up "incarcerated, and that cost will greatly exceed" the job training.

At various agencies, employes were predictably upset, especially at the proposed pay cut.

"I think it's a disaster," said David Friedman, 38, a neuroscientist at the National Institute on Drug Abuse. "I can't think of a better way to drive people out of government . . . I think it will take its greatest toll among the most motivated and creative people, because the ones who just want a job won't leave, the best people will leave."

"Personally speaking, I really need the money and a pay cut would really hurt," said a Commerce Department secretary, who has worked for five years and earns $15,000. She said she would not allow her name to be published because she feared getting fired.

A Republican appointee at the Small Business Administration said up to 30 percent of the agency was virtually useless and could be scrapped, but said the plan to eliminate the agency will "hurt the economy." She would not allow her name to be used, because her views anger her coworkers and supervisors.