Attorney General William French Smith appeared on Capitol Hill yesterday to throw the administration's support behind a tough revision of the federal criminal code, but he made it clear that there are no plans to provide additional funds to enforce the laws.

As President Reagan was in New Orleans unveiling his anti-crime proposals, Smith told the Senate Judiciary Committee, "As a whole, the proposed revision of the criminal code represents the most significant series of law enforcement improvements ever considered by the Congress." And he added, "The benefits. . . can be achieved without outlays of new funds."

Sen. Edward M. Kennedy (D-Mass.) warned the attorney general that the war on crime will need funding.

"The president is . . . calling for a new war against crime. That war has been declared again and again--and it has been lost over and over," Kennedy said. "If this latest war is to be more than words, more than a partisan slogan for the coming political year, then it is time for the administration to put its money where its rhetoric is. Talking tough is not enough."

"We are told these days that national defense is vital," said Kennedy, who has worked for years to get a criminal code reform bill through Congress, "and it is. But national defense begins in our own neighborhoods, where we must stop the reign of aggression by the muggers, the thieves, the robbers and the rapists. We cannot fight crime on the cheap--which is the hard lesson we should have learned in earlier years."

But Smith said the administration will be able to succeed without new funding because "we have been laboring for decades under a complex and inefficient criminal justice system . . . that has been very wasteful of existing resources."

The 400-page bill would simplify and reorganize a two-century accumulation of federal criminal laws, not only making them more easily understood, but also adding provisions aimed at violent crime, organized crime and drug trafficking.

It is the result of 15 years of debate and study, and earlier versions have been unable to survive both branches of Congress. The current version is thought to be considerably more restrictive than the one that died in the final days of the last Congress without coming up for a vote. House sources indicate it could face problems there.

Some of the more sensitive aspects of the package include provisions for mandatory prison sentences in cases involving drug trafficking or the use of firearms; clearance to hold especially "dangerous" suspects without bail; and abolishing parole provisions for most prisoners--all recommendations of the attorney general's task force on violent crime.

The president ignored the task force recommendations for stronger gun control laws and a plea that the federal government spend $2 billion in a four-year effort to relieve overcrowding in state prisons.

While he rejected spending $2 billion on new prisons, Reagan approved the use by states of vacant federal lands and abandoned military facilities to ease the overcrowding, and he began the program yesterday by allowing the General Services Administration to turn over an Air Force base at Watertown, N.Y., for use as a prison.

The only dollar outlay Reagan has proposed is a "responsible" federal system for compensating victims of crime. Along those lines, judges would be authorized to order convicted criminals to provide restitution to their victims.agraphics: WP photo by Frank Johnston. William French Smith, left, talks with Sen. Strom Thurmond (R-SC) center, and California ex-governor Edmund G. (Pat) Brown.