When Rebecca Mejia opened Tuesday's mail, the worry that had consumed her for a year suddenly disappeared.

The letter from the U.S. Immigration and Naturalization Service stated that the agency no longer considered her marriage a sham and that her husband would be eligible for an immigrant visa.

Mejia had married Marco Mejia, an undocumented El Salvadoran, two months after a November 1986 law decreed that all aliens who marry American citizens while in the midst of deportation proceedings must leave the country for at least two years.

Designed to discourage fraudulent marriages, the law made no exeption for those who married for love and not simply U.S. residency.

The Mejias' attorney, Cristobal Bonifaz, said the INS reversed its deportation order for Marco Mejia after deciding that the couple, who had lived together since early 1986, were common-law marriage partners before the law took effect. Couples married before Nov. 10, 1986, are not bound by the law.

"I think this will help those people who live in states that recognize common-law marriages," said Joseph A. Vail, a lawyer at Ayuda, a legal aid clinic in Adams-Morgan. "But those who live in states that don't recognize it are left out in the cold."

The District, where the Mejias live, recognizes common-law marriages. Virginia does not and Maryland recognizes only the common-law marriages of residents who moved from another state that recognizes such arrangements.

Rebecca Mejia said she worried all through her pregnancy and after her son was born six weeks ago that officials would suddenly arrive and escort her husband, a student and a waiter at a Georgetown restaurant who had entered the country illegally in 1983, to the airport.

"I just looked at the letter," Mejia said yesterday. "It had taken a year of my life; caused months of tension, of not knowing if my husband would be here when I delivered the baby. I love him so much. He's my life and the INS was trying to tell me I married him for money."

"We are not talking about whether marriages are good, bad or medium," said INS spokesman Duke Austin. "The law said if you marry a U.S. citizen while under deportation proceedings, you must depart the United States for a minimum of two years."

The immigrants granted legal status as spouses of U.S. citizens doubled from 78,000 in 1978 to 147,000 in 1986, according to INS figures. The marriages of as many as 30 percent of those 147,000 were thought to be fraudulent, Austin said.

J. Michael Myers, counsel for the Senate subcommittee on immigration and refugee affairs, said the law is imperfect and proposals are being drafted to change it. He said one possible remedy would be to allow those who get married while in deportation proceedings to remain in the country, but on probation for two years.

Austin said the INS needs some method of discouraging sham marriages, which are increasing and difficult to detect. "There are U.S. citizens who marry eight persons in one year for profit," he said.

But Marco Mejia said he is not one of those people marrying for the convenience of staying in the United States. Now he must reenter the country legally and go through the normal visa process.

"For a year I have been checking the mailbox, hoping the news would come," Mejia said. "I found someone I love and I want to have a life here. Now, finally, we received some good news."