On the eve of a crucial vote on a gay rights bill here. Elaine Noble the only avowed lesbian legislator in the country is on edge.

By normal indexes she shouldn't be. The bill has previously passed the state House and Senate and has the support of Gov. Michael S. Dukakis and other Massachusetts political heavies.

But in a very real sense the bill which could come to a vote in the state House this week has become a test of her effectiveness as a legislator. It also may set the stage for the nation's first statewide vote on the volatile gay rights issue.

"It's not a very threatening bill, but a lot of people are really nervous about," said the 33-year-old former college instructor. "Anita Bryant and her crew have gotten everyone uptight about gay rights."

When Noble, as a newcomer to the legislature sponsored a similar bill two years ago, it passed the House by 15 votes. As the first self-professed homosexual elected to sate office, she was an oddity then suspect in the eyes of her male and female collegues.

Now she's almost "one of the boys" in the clubby Beacon Hill statehouse atmosphere declared House Majority leader William Q. MacLean approvingly. "She's a good broad. She's a regular. There nothing phony about her."

"I like her. You can sit and have a beer with her," said MacLean a main stay in the House's conservative leadership. "When we have a late night session, she'll be in my office with all the guys having beer and pizza."

"Everyone looked at her kinda funny at first because they'd all read she was a lesbian," MacLean added. "The funny thing is she's very popular with the members now."

Noble, whose constituents in the Boston University area thought enough of her to re-elect her last fall, has run into hot water among gay groups and some liberals.

Their chief complaint is she hasn't spent enough time pushing gay causes. "They expected her to be a saint, and she turned out to be a politician," said Neal Miller, editor of the Gay Community News, a Boston weekly.

Noble, who grew up in a Pennsylvania mining town and holds two master degrees shrugs off such complaints. "People want you to sing and dance and juggle too," she said. "There's always someone around saying, 'You aren't doing enough for the cause.'"

She said the stakes over the gay rights bill have escalated dramatically since 1975. First, there's the national attention focused on the issue by Anita Bryant and the gay rights referendum fight in Dade County, Florida, last June. Then, there's the matter of a nonbinding referendum attached to the bill.

Noble and many of her legislative allies would like to delete the referendum from the bill because they fear it would result in an emotionally charged anti-gay campaign in Massachusetts next year.

"It would attract a statistically significatn percentage of the mentally unstable people in America," said state Rep. Barney Frank, a supporter of the bill. "People who make other peoples' sex lives their main priority are not well people."

Gay groups admit they'd almost certainly lose a statewide referendum dealing them a setback like the one they received in Florida where Dade County voters overwhelmingly repealed a gay rights ordinance. Noting a petition drive is already under way to put the matter on a statewide ballot in California, they fear it would lead to even more such tests.

"Anytime you lose it looks bad," Noble said. "We don't have the economic or psychic energy to fight in California. Massachusetts and every place else."

"Dade County put all of us in a great bind," she continued. "It brought gay rights issues more into the public eye, and made them more controversial."

The bill in the state legislature is not as far reaching as the ordinance repealed in Dade County. That one banned discrimination against gays in housing employment and public accommodations. The one here involves only employment in state jobs.

But it has created many of the same fears. "I'm against it because I don't think any immoral action can be made moral by a piece of legislation," said Rep. Marie Howe a Democrat. "What we're afraid of is that it will lead to a setting up of a quota sysltem in hiring."

Noble was victim of some of the same uneasiness after her first election in 1974. One group planned - but later dropped - an attempt to stop her from being seated on grounds that homosexuality is illegal in the state. Her car was vandalized so many times that she started riding a bike to work. And at one point she asked a fellow legislator who had made a crude remark. "Does the representative feel that homosexuality is catching? And if so is he afraid he'll catch it?"

Regardless of what happens to the gay rights bill this week. Noble's political future is in doubt. Redistricting has cut the number of seats in the House, and placed her in the same district as Frank, her fellow liberal Democrat. So she's at looking at other offices. One possibility is the Boston City Council.

"I like politics and I want to continue in political life," she said. "I just haven't decided what office."