The D. C. Law Revision Commission yesterday gave final approval to a new basic criminal code that is modernized to meet the needs of an urban center and includes new, more restrictive procedures for sentencing offenders.

The commission's recommendations will be sent to Congress, which must approve the new code - called the D. C. Basic Criminal Code Act of 1978 - before the proposal becomes law.

"It's very hard to wax sentimental over a criminal code," Chairman Stephen I. Danzansky observed yesterday as he thanked the commissioners, who worked nearly 4,000 hours to overhaul the current turn-of-the century criminal code.

"Now we leave our child in the hands of Congress . . . be gentle with it . . . " Danzansky said.

Generally, the proposed act defines basic crimes against persons and property, such as homicide, robbery and burglary; outlines set prison terms based on kinds of offenses, and mandates a procedure by which judges will detrmine sentences based on several factors.

One section of the act is designed to modernize the language of the laws and tailor them to the needs of a densely populated city that is also the nation's capital.

For example, the proposed new laws set heavy penalties for the theft of welfare checks and makes it a specific crime to interrupt the service of public utilities, such as the Metro subway system.

One section of the new code would prohibit damage to a "public treasure," such as a historic document or a monument. Such an offense is classified in the proposed as a felony that would carry a penalty of not less than 18 months and not more than 42 months in prison. The charge would be reduced to a misdemeanor if the property could be restored to its original condition for less than $500, according to the commission's recommendations.

For the first time, the city would have a specific law that would prohibit terrorism and hostage taking, whether or not the acts was politically motivated.

The proposed new laws or free of any references to victims or defendants by sex with words used as "persons" or "actors" used instead. The term "sexual assault" is substituted for the word "rape," which commissioners felt had a clear male-female connotation.On possible effect of the change in termino ogy and definition of the crime of sexual assault would be to allow consenting adult homosexuals to live together without fear of arrest.

The new sentencing provisions come close to a system of fixed prison terms while at the same adjusting punishment to fit the offender.

The proposal attempts to limit the judge's discretion by setting up specific-term sentences for various "grades" of crimes. For example, under the proposed law, first-degree homicide is a "Class A felony" that carries a prison term of not less than 12 and not more than 16 years in prison.

If a sentence is imposed outside of that range, the judge's decision can be appealed by either the defendant or the prosecution. The new law sets maximum prison terms above the range for each grade of crime. For example, the most in the case of first-degree homicide, the most serious of all offenses, the maximum prison term is 20 years.

However, the commission allowed for life prison terms, with no possibility of early release, if for example the defendant has a serious prior record, if the victim was mutilated before death, or if more than one person was a victim of the crime.

The overall effect of the new sentencing provision is to eliminate the possibility of parole in all categories of offenses. That commission decision reflected current throuht among legal commentators who believe that parole boards often are arbitrary and frequently are manipulated by prisoners who want early release.

The new proposed law does provide a system whereby prisoners can accumulate so-called "good time" for each month of good conduct in prison, and thus reduce their sentences.

In all but the most serious classes of felonies, the commission recommended that judges take various factors into consideration before they sentence offenders.

For example, if a defendent offers to make restitution for his offense, the judge should consider reducing jail time included in a sentence. If the defendant used a dangerous weapon during a crime, however, that is a factor that should ten120d toward a prison sentence.