what is differnce between the state and federal worker's compensation plan?

That depends upon the state.

why is it neccessary to have both federal and state compensation plans?

The difference between state and federal worker's compensation plans lies in the jurisdiction and the level of coverage provided.

State Worker's Compensation Plan:
1. Jurisdiction: State worker's compensation plans are established and administered by individual states in accordance with their specific laws and regulations.
2. Coverage: These plans provide benefits to employees who suffer work-related injuries or illnesses, regardless of who was at fault. Benefits typically include medical expenses, lost wages, disability benefits, rehabilitation, and vocational training.
3. Administration: Each state has its own agency or commission responsible for overseeing the worker's compensation system and ensuring compliance with state laws.

Federal Worker's Compensation Plan:
1. Jurisdiction: Federal worker's compensation plans are administered by various federal agencies for specific categories of workers. Each agency has its own set of rules and regulations.
2. Coverage: These plans provide benefits to federal employees who suffer job-related injuries or illnesses. The coverage may vary depending on the agency and the type of work being performed. Federal worker's compensation may also cover longshoremen, coal miners, and certain other workers who fall under federal jurisdiction.
3. Administration: Federal worker's compensation plans are administered by specific agencies such as the Office of Workers' Compensation Programs (OWCP) for federal employees, the Longshore and Harbor Workers' Compensation Program (LHWCP) for eligible longshoremen, and the Black Lung Benefits Program for coal miners.

To determine the specific differences and benefits offered by state and federal worker's compensation plans, you will need to consult the relevant state laws or federal agency guidelines. This information can typically be found on the respective state's government website or the website of the federal agency involved.