A fractious five-year fight to revamp Virginia's sexual assault laws ended today with passage of a bill designed to reduce the trauma that often confronts rape victims who prosecute their attackers.

But the last day of the General Assembly's regular 1981 session turned out to be one of the dullest in memory, with little of the dramatic, clock-racing decision-making to keep legislators toiling into the night. Most of the lawmakers had so much time on their hands, in fact, that they sat distractedly at their desks or roamed the corridors of the Capitol, bemoaning the lack of any controversial, serious business.

Even the rape measure's unanimous approval in the House of Delegates was in marked contrast to the highly charged debates the issue has set off in past sessions. Legislators who had shepherded the bill through numerous compromises and rewrites heralded its final version as a definite improvement over current law.

"This will encourage rape victims to report the crime and protect them from a lot of the emotional strain they now can face if they go to court to punish their assailant," said State Sen. Frederick C. Boucher (D-Washington), the bill's chief sponsor. He said he expected Gov. John H. Dalton to sign the measure.

Though the legislation falls far short of more sweeping reforms proposed in 1977 following a task force study, it would outlaw the introduction of evidence about the victim's reputation for chastity and establish several new sex-related crimes, including penalties for homosexual rape and sexual assault with an inanimate object.

From a prosecution standpoint, the bill would presumably make convictions easier to obtain by removing a requirement that rape plaintiffs show they physically resisted their attackers or cried out for help. A defendant could refer to an alleged lack of resistance but it would not automatically assure an acquittal.

Several prosecutors had complained about a provision in the bill that would allow a rape defendant to introduce evidence of other sex acts by the victim, but Boucher said the defendants would first have to show in a closed-door hearing that the alleged victim had a motive to fabricate charges against the defendant.

Most of the House and Senate disagreements over legislation were settled harmoniously. A notable exception came when House leaders refused to go along with a Senate resolution condemning acts of terrorism and specifically rebuking the Ku Klux Klan and the Nazi and Communist parties. s

The Senate had unanimously endorsed the resolution, but the House Rules Committee objected to citing any particular group by name. State Sen. Joseph V. Gartlan Jr. (D-Fairfax), the resolution's sponsor, complained in the waning minutes of the session that two House members who could have enabled the measure to pass instead "fled from the floor of the House and disappeared."

"To the people who asked me to sponsor this resolution, I'm sorry," said Gartlan. "For the view they will now take of this legislature, I blush with shame."

In other final action, a bill that would make it a felony to sell minors paraphernalia for use in taking drugs emerged from legislative conference in a compromise form and was easily approved. An earlier version had run into last-minute problems because it was held to be a virtual copy of a law recently declared unconstitutional.

Northern Virgnia legislators had been eager to have the new law approved because Maryland already has a similar law and some lawmakers had expressed fears that the absense of a Virginia law would drive sellers of drug paraphernalia from Maryland into Virginia suburbs.

With time on their hands, the legislators held congratulatory ceremonies and presented closing-of-the-session gifts to both House Speaker A. L. Philpott and Lt. Gov. Charles S. Robb. Indeed, things became so boring for House's often bawdy Majority Leader Tom Moss (D-Norfolk) that he was seen on the floor guffawing over photos of a partly nude Rita Jenrette, the estranged wife of a former South Carolina congressman.