Virginia state Sen. Frederick C. Boucher (D-Washington) had barely walked into the committee meeting today when he felt the full force of "the hot box."

It was the last day the House Courts of Justice Committee would consider any Senate bills, and the committee members were launching their traditionally frenzied attack on the legislative backlog. With measures rapidly being killed or held over until next year, "hot box" describes the process.

It created a now-or-never situation for Boucher, who was trying to convince a panel full of lawyers that they should approve his bill revamping the state's sexual assault laws.

"I've been available for three days to discuss this bill," he angrily told the committee, whose members were taking turns pointing out flaws in the legislation. "We've considered this issue for three consecutive sessions, and I submit to you that the time has arrived to act."

By day's end the committee had acted. Boucher's bill was dead for another year.

Other casualties of the "hot box" system that were dispatched in a matter of minutes:

A bill to extend the death penalty to persons convicted of mass murder.

A measure to establish special judgeship selection commissions.

Legislation to give juries more information about a convicted felon's history prior to sentencing.

Considering the quick, almost cavalier manner in which the House committee scuttled Senate legislation today, Boucher's bill hung on longer than most. It took two committee meetings, several heated exchanges between the bill's supporters and opponents and the panel's well-known penchant for parliamentary confusion to put the measure to rest for the year.

"I for one do not want to rewrite the state's sexual assault laws in this atmosphere," complained Del. Theodore V. Morrison Jr. (D-Newport News), who had met with Boucher over the weekend to redraft the bill so it would be more acceptable to the committee.

Boucher argued, however, that Morrison, a defense attorney, was more interested in making the bill acceptable to defendants in rape cases. He accused the delegate of trying to amend the bill in a way that would discourage rape victims from going to court against their alleged attackers.

"I'm mad as hell, and you can quote me," the normally mild-mannered Boucher said afterward. He was so furious at what he called the committee's "improper" treatment of him and his legislation that he did not bother to attend the final meeting in which his bill was officially "carried over" until next session.

What particularly rankled Boucher, he said, was "Ted's insistence on using the bill to open up the use of a victim's prior sexual activity" by allowing evidence of a defendant's past sexual acts to be presented in court.

"We're trying to encourage women to report the crime of rape, which is the most underreported crime today," Boucher, 34, said.

While Boucher urged the measure's approval, saying the bill was a much weaker version than one the House committee passed last year, Morrison and other opponents pronounced the bill "a mess" and said it should be studied further.

Del. J. Samuel Glasscock (D-Suffolk) noting that the bill would not become effective until July 1981, urged the committee to pass the measure "to tell the world that we really are interested in this issue." He said the panel could clean up problem areas next year.

"If the bill is not in good shape, it's probably an indictment of the way the committee has approached the subject," Glasscock said.

Both Glasscock and Del. Bernard S. Cohen (D-Alexandria) accused opponents of the bill of not treating the measure seriously, with Cohen complaining that "an awful lot of Mickey Mouse was going on" when the committee had discussed the bill earlier in the day.

Initially the bill's opponents had been unable to muster enough votes to kill or carry over the legislation. But when supporters tried to force a vote to send the bill to the full House, committee chairman Del. George E. Allen Jr. (D-Richmond) abruptly recessed the meeting.

"How can you take a vote when the members are leaving?" asked Allen, who frequently looks to Morrison and others for guidance on how to conduct the committee's sessions.

Since Morrison was one of several committee members who left to attend other meetings, Allen paid no attention when Boucher supporters asked to take a vote to approve the bill.

Glasscock and Boucher later expressed skepticism that the committee would seriously study the bill during the next year. They argued that a similar bill had passed both the House and Senate last year only to die in conference on the last night of the session when opponents said the legislation needed more careful examination.

In other assembly action the Senate unanimously passed tonight a bill that would allow Reston to set up a limited form of town government. Earlier this week the House approved legislation that would allow Reston's 37,000 residents to hold a referendum this fall to decide whether that community should elect a mayor and town council and have the power to impose limited taxes.

The Senate also passed a bill that would require annual auto emission inspections of cars registered in Northern Virginia. Reluctant legislators passed the bill, effective in 1982, only after the Environmental Protection Agency threatened to cut off more than $100 million in federal air pollution funds.

Last month the House passed a watered-down version of the controversial bill, which was strongly opposed by automobile and business interests. Because the House and Senate passed different versions of the bill, the differences must be resolved in a conference committee before the legislation is finally approved.