A fragile coalition of women's groups and religious organizations, drawn together to fight federal cuts in welfare benefits for pregnant women, nearly fell apart here last week after a behind-the-scenes debate over the how to define the fetus in the womb.

The controversy, one of semantics, has resulted in two pieces of legislation and an uncommon degree of tension between normal political allies. By State House standards, it is an unusual dispute and one that reflects the capricious nature of legislation related in any way to the abortion issue.

However stormy the controversy, it has not blurred the coalition members' shared goal of restoring benefits--cut by the federal government--to women in their first six months of pregnancy. Nor has it interfered with the progress of the bills in the General Assembly.

"At this point I don't really care which bill passes," says Del. Anne Perkins (D-Baltimore), sponsor of a House version that would provide general public assistance grants to pregnant women. "We just want these women to have some help. It was ill-considered (by the Reagan administration) to take away these grants."

The debate over language erupted several weeks ago when representatives of groups ranging from Planned Parenthood to Associated Catholic Charities came together to work on legislation to help pregnant women make up for federal funds that were cut October 1.

All of the groups agreed that women in the early stages of pregnancy who lack proper nutrition and medical care are more likely to have low birth-weight or mentally retarded babies. And they agreed that the federal cuts were denying welfare grants of about $82 each month to 598 pregnant Maryland women and the "fetuses" (or "unborn children," depending on which side of the linguistic debate) developing in their wombs.

Although the Catholic Church normally splits with women's groups on abortion issues, its lobbyists here are the leaders in pressing for aid for the underprivileged. And like some other antiabortion groups, the church lobby believes that restoring benefits to pregnant women would discourage them from seeking abortions.

Women's rights groups, such as the National Organization of Women, and Planned Parenthood, which are "pro-choice," also favored restoring the benefits, but for different reasons. They said the funds would assure proper food and medical care if the women chose to go ahead with the pregnancy.

Then the trouble began.

"We and others became concerned about the language," explained a representative of Maryland Planned Parenthood. "The bill started out (with the fetus) being identified as an 'unborn child' the term supported by the church lobby ."

"We were very upset about using 'unborn child,' " said Esther Levin of Maryland NOW. The problem with that definition, according to the pro-choice groups, was that it lent credibility to pro-abortion groups that are pushing for a Human Life Amendment in Congress and always have argued that human life begins with conception. The pro-choice groups wanted to use the term "fetus."

So members of the coalition argued, discussed and considered other options. Perkins suggested "conceptus." The church lobby frowned.

"Language is so powerful, that is why it was such a big issue," said the official from Planned Parenthood. "But it was really encouraging to see so many groups trying to work it out."

What eventually evolved were two bills proposing different kinds of grants. The first, sponsored by Republican Sen. John A. Cade of Anne Arundel County, would provide welfare benefits for "the anticipated child and pregnant natural mother." The measure, which the Senate Budget and Taxation Committee approved Friday, would cost the state $826,000 in 1983 and would provide a maximum monthly grant of $230 for the mother and her "anticipated" child.

Bishop J. Francis Stafford, auxiliary bishop of the Archdiocese of Baltimore, testified in support.

While the women's groups said they agree with "the intent" of Cade's measure (and some of the groups testified in favor of it), they still were wary of the terms "anticipated child" and "pregnant mother." Some worried that the legislation would not provide grants to women who were pregnant for the first time.

An alternative measure, sponsored by Perkins, which the church neither supports nor opposes, proposes using General Public Assistance grants paid directly to "pregnant women." Under her measure's provisions, which would cost the state $440,000 in the first year, the "anticipated child" receives no grant and therefore does not have to be defined in the bill.