Benefits paid federal and postal employes who become seriously ill, are injured or killed jumped more than 300 percent since 1970 -- to $345 million a year -- according to a new congressional report.

Auditors for the General Accounting Office believe that the big jump in disability claims and payments resulted in part from overly generous interpretations of federal rules that spell out benefits due employes. GAO was especially critical of erratic and sometimes conflicting decisions to pay or deny benefits for alleged work-related disabilities.

GAO, the congressional watchdog agency, recommended that the Labor Department which administers the federal disability program tighten up its rules. Labor Department already has a task force working in that area.

GAO said the government should develop better guidelines to determine what is a "compensable injury," particularly to spell out when illness such as heart, cancer or mental disorders are work-related.

Federal workers who are ruled totally disabled can receive tax-free payments amounting to a maximum of 66 percent of salary, with regular cost-of-living raises. At current levels those payments range from a minimum of $464 per month for lower grade employes to $2,969 for top-paid civil servants.

Non-cash benefits for workers who are injured or become ill because of their jobs include payment for medical services, medical appliances, supplies, payment for transportation to treatment and vocational rehabilitation costs.

GAO took note of the fact that many federal workers, officials and members of the public have seriously criticized the application of the federal disability program. Some employes claim legitimate benefits are denied, or that "buddy systems" in agencies grease the way for disability retirements for healthy or uninjured workers. There have also been charges that some agencies use forced disability retirement -- particularly for mental disorders -- to get some workers off the payroll, at the expense of the taxpayers.

In addition to the big jump in claims and payments for illness, death and injury, GAO noted the following increases between the 1970 fiscal year and fiscal 1978:

Annual injuries jumped 72 percent, from 120,625 to 207,615.

Annual claims increases by 70 percent, from 17,795 in 1970 to 30,301 in 1978.

The number of people drawing long-term compensation jumped by 90 percent, from 23,462 to 44,576.

Benefits paid out on an annual basis rose from $131 million to $545.8 million in seven years, a 315.1 percent increase.

GAO said a "lack of uniform policy and adequate guidelines" on the relationship of heart disease to the job has often resulted in seemingly arbitrary determinations whether the employe is compensated or not. It cited two cases:

First, a 40-year-old postal mail handler who had a heart attack at home, on a non-workday.He claimed his job of lifting heavy mail sacks contributed to the heart attack.

A federal board denied the mailman benefits after a medical specialist said the employe's usual work was not a factor in producing his heart attack.

In a similar case, a 57-year-old mechanic for the U.S. Forest Service died following a heart attack. His widow claimed that a job-related head injury he suffered nine months earlier contributed to his death. Benefits were ordered for her after a neurosurgeon testified that it was possible a head injury could cause sufficient stress "so as to make a 'weak heart' give up and die."