The Senate, struggling to complete work on a five-year renewal of the Superfund toxic-waste cleanup law, yesterday rejected an experimental project to compensate victims of exposure to hazardous waste.

The project was deleted from the bill, 49 to 45, after opponents argued that the $30 million-a-year experiment would quickly outstrip the government's ability to pay for it.

The Senate halted action on the bill just short of a final vote as approaching sunset signaled the beginning of the Jewish holiday of Yom Kippur. But passage of the measure appeared certain when lawmakers return Thursday, including a controversial broad-based tax on manufactured goods that has drawn outrage from industry and a veto threat from the White House.

Industry groups and the Reagan administration also had lobbied heavily against the victims' compensation provision, which would have authorized a demonstration project to provide medical help for persons believed to have been injured by exposure to toxic waste.

Its main proponent, Sen. George J. Mitchell (D-Maine), argued in vain that the provision was a "cautious, limited effort" to determine the need for victims' assistance. "This is not an entitlement program. This is not a national health insurance program," he said. "Those who now say 'Kill this provision,' are in effect saying, 'Do nothing.' "

Opponents disagreed, contending that the program would be virtually impossible to contain. "The plain and simple fact is that the Treasury cannot afford the great expenditures that this program is likely to incur," said Sen. William V. Roth Jr. (R-Del.).

The Senate bill would provide $7.5 billion to clean up toxic waste sites over the next five years, a nearly fivefold expansion of the current $1.6 billion law that would be financed in large part through a value-added tax on large manufacturers.

The White House adamantly opposes the tax, and many lawmakers are uncomfortable with it as well, on the grounds that it will have the greatest impact on those least able to pay. But they narrowly defeated, 46 to 48, an effort to exempt fertilizers and animal feeds from the new tax despite pleas from farm-state senators that hard-pressed farmers could not afford the added burden.

Proponents argued that the exemption would trigger an avalanche of requests for special treatment from other industries.

"If agriculture is hurting, are textiles not?" said Finance Chairman Bob Packwood (R-Ore.). "It would be a tragedy if we started down that road."

Lawmakers also approved an amendment designed to speed cleanups by granting releases from liability to polluters in certain cases. The provision, a compromise that was accepted without dissent, is opposed by environmental groups who contend that it would encourage polluters to move their wastes to new landfills instead of treating them permamently.

"We think people should be responsible for their waste as long as it's hazardous," said Leslie Dach of the National Audubon Society.