Elizabeth Taylor said she'd tried to talk to President Reagan about plans to combat AIDS, but told a rapt audience with a laugh yesterday, "He was so tacky -- he left town."

Instead, she settled for a National Press Club lunch, preceded and followed by lobbying in the halls of Congress, which she knows well from the years she was married to Sen. John Warner (R-Va.).

At the press club, Taylor was costumed for Noel Coward, but spoke as if playing Joan of Arc. Before she was finished, the normally blase' press cheered her as though they were conscripts in her crusade against AIDS.

She spoke without notes, the words tumbling out, almost knocking each other over, and as national chairman for the American Foundation for Aids Research, called for help for AIDS victims and their families.

"Accurate information is currently the only weapon we have to stem the tide of this growing epidemic," she said. On the hot question of testing for AIDS, she said her foundation "believes that voluntary and confidential testing is in the best interests of our nation's public health." She opposed discrimination against people who test positive for AIDS antibodies.

Taylor called for the establishment of an international AIDS coordinating organization. "We must win, for the sake of all humanity," she said.

Taylor showed a lively wit, even at her own expense, and a thorough knowledge of AIDS facts in her answers to questions from the audience.

About mandatory AIDS testing for marriage license applicants, the seven-times-married Taylor paused a moment, laughed, and said, "Well, it's been a long time since I was married -- do they still require other tests?"

When assured other blood tests are still mandatory, she said she could see some reason in tests "if there's a chance of passing AIDS on to a child."

As for occupational hazards in love scenes for the movies, Taylor said, "It is called 'acting.' After all, in 'Macbeth,' we don't use real knives and daggers. There are ways of portraying passion, how shall I say, ways of portraying deep kissing, without being that involved. You can have lots of help from camera angles. I believe that at first, people in our business overreacted." (Concern had been expressed, after Rock Hudson was diagnosed as having AIDS, about an actress who'd played a love scene with him.)

Taylor, whose life has often been viewed as one glamorous love affair after another, said she thought movie industry people were changing their ways of living in response to the dangers of AIDS. She said she thought the end had come for singles bars. "We have to grow up."

Actors apparently are not the only people worried about AIDS. "Two years ago, I lost a job to do a commercial for a soft-drink firm, after they learned I was chairman of the American Foundation for AIDS Research," Taylor said.

Her involvement began when she was asked to be chairman of a fund-raising dinner. "It was extraordinary how many didn't want to have their names connected with it. AIDS was a taboo subject. It took seven months, but we did get 1,000 honorary patrons. It would blow your mind, the people who wouldn't help. I was incensed and personally frustrated."

Taylor said it was several months later that she learned about Hudson's illness.

Though she's spending much of her time promoting the foundation, she said, "my career is staggering along."

The bulk of her speech was serious, but she began with one joke: "I must admit that I do not usually welcome the opportunity to speak to members of the media," said Taylor, known for her frequent efforts to elude the press.

(Another humorous moment had come just before. As press club President Andy Mollison prepared to introduce Taylor, he said he had one "scoop." Reminding the audience that a $718 bill owed to the club by the organization Americans for Hart had been paid, he offered an update: "The check was returned stamped 'insufficient funds.' ")

Earlier, Taylor had slipped into the VIP reception, where she was immediately surrounded, according to other guests. She came to the head table after most other guests had finished their meals.

So she missed a man in a baseball cap and a sports shirt. He stood by the head table and held up a large placard reading: "Quarantine Manhattan Island ... the AIDS Capital of the World." The television cameras, with nothing else to do, had plenty of time to film him before he was escorted to the door by a club staffer.

When Taylor, in a black-and-white suit with polka-dot scarf, took her place in the limelight, her necklace and rings sparkled. But lest her nose also shine in the heat of the television lights, she pressed a folded bit of Japanese rice paper against her face.

Though she was once known for her appetites, she is now so thin that no one at the luncheon was surprised when she took only a bite from her fruit-and-cottage cheese plate.

The chef at the Vista Hotel, where she's been staying during the AIDS conference here this week, said she's only eaten melon, broiled fish, asparagus, radicchio -- and, her only indulgence, a croissant for breakfast.

The Presidential Suite, where she stayed, has a fully stocked bar, but it was not touched. The hotel did have to replenish the iced tea and Evian and Perrier sparkling waters. In deference to her Spartan regime, the Vista, which last time sent sweets to the suite, this time delivered her from temptation with a fruit basket.

Though actor George Hamilton canceled the room reserved in his name, he thrilled the women at the front desk by stopping to jolly them up one morning as he walked through the lobby.

Taylor's resident entourage included Chen Sam, her personal representative, and her hairdresser, Jose' Eber, who . were housed in three bedrooms. Taylor's own room included an adjustable bed, originally bought for Senegalese President Abdou Diouf, as well as a living/dining room and a kitchen.