THE SENATE'S approval last month of a partial ban on semiautomatic assault weapons was both the biggest defeat NRA leaders have suffered in that body and the most important action sought by law enforcement officials in this Congress. The fact that a majority of senators -- on two roll-call votes -- approved important distinctions between these weapons of crime and the firearms of sport and other personal uses is a significant endorsement of a solid anticrime measure. But at this point it is buried in bad baggage, as one part of an overstuffed bag of proposals in the name of crime-fighting. Democrats as well as Republicans would like to be on record this year as supporting an omnibus crime bill. But given all the bad stuff in this package -- not to mention some 330 amendments -- the Senate should abandon it.

Among the provisions is authorization of the death penalty for 30 federal crimes, primarily murder, espionage and treason. A sizable majority of the Senate supports a broader death penalty. Most of the offenses carry the penalty already, but the actual sanction was invalidated in 1972 when the Supreme Court struck down all existing state and federal capital punishment laws and later set forth guidelines for the way such punishment may be imposed. We continue to believe on moral grounds that the death penalty is abhorrent no matter what the circumstances of the offender or the nature of the crime.

The crime package also has a provision that would permit use of illegally seized evidence in trials under certain circumstances. This would be dropped under a tentative agreement reached during efforts to come up with something that could spring the crime bill for approval. The bill also would limit the number and duration of appeals by prisoners on death row, in effect speeding the capital punishment process. How these proposals might emerge from slapdash amendment surgery to get the package is a disturbing prospect.

In fact, what the Senate has is a collection of proposals that should be, and in some cases have been, considered separately. The NRA leaders may find temporary relief and a thin claim of success in any delay of the assault-weapons ban, though the Senate has spoken on this and could speak again. Taken as a whole, the crime bill is more than Congress should try to enact between now and when it comes time to bolt for the campaigns.