In the court of public opinion, Rep. Anthony Weiner (D-N.Y.) already appears to have been convicted of, at the very least, breaking his marriage vows, misleading his constituents and lying to the media.

But if the case ever gets before a smaller jury — the members of the House ethics committee — the verdict may be less clear.

Weiner is facing increasing pressure from colleagues to resign his House seat in the wake of his admission that he sent a lewd photo to a Seattle college student via Twitter and engaged in inappropriate electronic exchanges with other women.

Weiner has ignored those calls, reiterating Thursday that he does not plan to quit. “I’m going to get back to work as best I can,” he told the New York Post.

Within hours of Weiner’s public confession Monday, House Minority Leader Nancy Pelosi (D-Calif.) called on the Committee on Standards of Official Conduct, as the ethics panel is formally known, to launch an investigation. The panel issued a statement the next day, saying, “If and when an investigation is appropriate in any matter, the committee will carry out its responsibilities pursuant to our rules.”

But which rules, exactly?

The word “Twitter” does not appear in the House Code of Official Conduct, nor does “direct message” or “explicit photo.” Infidelity is not referenced, either, and while the means of communication may be new, lawmakers have generally been wary of policing each other’s sexual behavior.

“If the only evidence out there . . . clearly indicated that this was personal conduct only between consenting adults, I just don’t see a reason why the ethics committee would or should take it up,” said Robert L. Walker, the former staff director of both the House and Senate ethics panels. “Even if people think it’s reprehensible conduct, that doesn’t mean it’s an ethics violation.”

The House does have guidelines governing “official electronic communication content,” and rules permitting lawmakers to post content on external Web sites for “official purposes,” but it’s not clear whether Weiner’s Twitter account falls under those categories.

Like many lawmakers, Weiner tweets a mix of personal and political observations. His Twitter user name — @RepWeiner — identifies him as a member of Congress. But his Twitter page links to his campaign Web site, not his official House site.

“We’re in the Twitter era. . . . But the technology shouldn’t drive the decision,” Stanley Brand, an ethics lawyer, said this week. “The House could render a service, saying: ‘This is what you can do online, and this is what you can’t do.’ ”

Experts said Weiner could be vulnerable on three fronts: Did he use any government resources to conduct his behavior? Were any of his interactions with underage women? And did his actions not “reflect creditably on the House”?

The House members’ handbook permits personal use of House equipment and supplies only “when such use is negligible in nature, frequency, time consumed, and expense.”

At his news conference Monday, Weiner said, “My BlackBerry’s not a government BlackBerry. My home computer is usually where I did these things. I don’t have a knowledge of every last communication, but I don’t believe that I used any government resources.”

Weiner may not have broken any rules even if he was in the Capitol or his congressional office during these exchanges.

“Sitting in your chair in the office while you’re doing personal activities does not raise a violation of the rule on use of official facilities,” said Kenneth A. Gross, an ethics and campaign law expert at Skadden, Arps, Slate, Meagher & Flom.

During Monday’s news conference, Weiner was also asked whether any of the women with whom he corresponded might have been underage, or lied about their ages.

“Of course no one ever knows that,” Weiner responded. “But I know that I never had any intention of having an interaction with underage women, and no information that I have now shows that I did.”

If the ethics committee discovered that any of Weiner’s behavior violated federal laws governing communication or sexual relationships with minors, the panel could make a referral to the Justice Department.

Inappropriate behavior toward minors was at the heart of the scandal surrounding Rep. Mark Foley (R-Fla.), who resigned in 2006 after sending explicit electronic messages to teenage House pages. In that case, Foley quit before he could be punished by his colleagues, but the ethics panel did investigate whether any House leaders or officials knew about Foley’s behavior.

More broadly, House rules dictate that a House member or employee “shall conduct himself at all times in a manner that shall reflect creditably on the House.”

In the past, the ethics panel has invoked the clause to criticize members for behavior ranging from violating House gift rules to fixing parking tickets to threatening to retaliate against a colleague because of a vote. Typically it has been used only if members violated the law or abused their official position.

“Some might call it a vague provision,” Walker said. “I think the way to look at it is that it’s a deliberately open-ended provision. . . . There is always something new under the sun”

Ultimately, if Weiner stays in the House, the voters in his district may punish him next year, even if the ethics panel doesn’t.

“I don’t think it’s a violation of a rule or law,” Brand said. “There are some actions where political or electoral sanction is the only remedy.”

Staff writer Paul Kane contributed to this report.