MPs are concerned prosecutors are opting for lesser charges
Government claims that victims of crime are at the heart of the criminal justice system have raised "damaging" expectations, says a report by MPs.
The House of Commons justice committee said victims who thought prosecutors in England and Wales were their champions would "inevitably be disappointed".
The MPs also called for measures to help victims and witnesses with mental health problems to give evidence.
The Crown Prosecution Service said it had clarified the prosecutor's role.
The report focused on the work of the Crown Prosecution Service (CPS) in England and Wales.
"The prosecutor's role in relation to victims... seems to be generally misunderstood," it said.
"The prosecutor is not able to be an advocate for the victim in the way that the defence counsel is for the defendant, yet government proclamations that the prosecutor is the champion of victims' rights may falsely give this impression.
"Telling a victim that their views are central to the criminal justice system, or that the prosecutor is their champion, is a damaging misrepresentation of reality.
"Expectations have been raised that will inevitably be disappointed."
The committee called for a review by Attorney General Baroness Scotland into charging decisions, because of concerns prosecutors were opting for lesser charges to secure convictions.
Head of the CPS, Director of Public Prosecutions Keir Starmer, said a document published last month "conveys our vision, gives clarity to the role of the prosecutor and raises debate about the future of criminal justice".
"It sets out a coherent way forward, explaining our work so that it can be clearly understood by the public," he said.
The service aimed to become more responsive to community needs while maintaining consistent standards nationally, he added.
"Fair, fearless and effective; open, honest and transparent; protective, supportive and independent: these are the qualities that the public has a right to expect of its public prosecution service. We are determined to meet those expectations."
Baroness Scotland said: "I share the justice committee's views on the need for clarity about the aims and purposes of the CPS and about the need for joint working across all the different prosecuting authorities."
She chairs a strategic board to improve and modernise the prosecution service, which she said had "achieved much" in the last two years.
"There is more to do but I am very confident we can and will, together, go further and do more."