Sen. Edward M. Kennedy (D-Mass.) and Rep. Fortney H. (Pete) Stark Jr. (D-Calif.) unveiled a far-reaching package of health care revisions yesterday, saying they were "fed up with fighting a rear-guard action" against the Reagan administration's cuts in medical services to the poor.

Stark, chairman of the House Ways and Means subcommittee on health, said that parts of the package have bipartisan support in the committee, and that he hopes to have them incorporated into this year's budget reconciliation bill. Republican sources said Stark will probably get substantial bipartisan support on several of the provisions, since Reps. Willis D. Gradison Jr. (R-Ohio) and W. Henson Moore (R-La.) have developed similar proposals in the past.

The Kennedy-Stark plan would:

* Allow about 4 million workers who have been laid off from their jobs to retain health insurance coverage under their former employers' plans by paying the full premiums themselves. About 5 million widows, divorcees and children would be given similar rights when they lost their health insurance through death or divorce. In addition, states would be encouraged to establish subsidized insurance pools for those who can't afford costly individual private policies.

* Prohibit hospitals from denying emergency service to people who genuinely need it, on pain of criminal or civil penalties. At the same time, hospitals treating a high proportion of poor people would receive higher Medicare payments. The government would study whether to give inner-city hospitals higher payments to reflect higher wage costs.

* Slow the annual rate of increase of the $400 first-day hospital payment for Medicare patients, as well as copayments for nursing home care, by permitting the rates to rise only as much as the government's payment to hospitals rises each year under Medicare. Kennedy said this provision would reduce beneficiary payments for Medicare services by $600 million a year.

* Stop paying private hospitals a return on equity under Medicare, which Kennedy said would save $200 million a year. In addition, Medicare would experiment with a fixed payment for doctors, set in advance and based on the complexity of the case, for in-patient services provided under Medicare. DISABILITY UPDATE . . . Sens. Carl Levin (D-Mich.) and William S. Cohen (R-Maine), the Senate sponsors of last year's Social Security disability reform bill, have fired off an angry letter to Acting Social Security Commissioner Martha A. McSteen, complaining that the regulations implementing their law make it much tougher to stay on the disability rolls than they had intended.

Levin and Cohen said the provision barring Social Security from removing a beneficiary from the rolls unless there is demonstrable improvement in his medical condition has been subverted by the proposed regulations. They added that, in some respects, the rules are "clearly opposite to the intent of Congress."

Groups representing the disabled have made similar complaints in recent weeks and McSteen has pledged to take a thorough second look at some of the regulations before they become final.