Woman's slant on long trip west; Women's Diaries of the Westward Journey, by Lillian Schlissel. New York: Schocken Books. 272 pp. $16.95.

Invariably it was the men who made the decision to go west, seeking land, work, and gold, 1840-1867. ''O, let us not go,'' one woman screamed in italics in her diary, apparently speaking for all emigrating wives, mothers, and sisters.

In this unique book, Prof. Lillian Schlissel, director of American Studies at Brooklyn College, has moved scholarship ahead by two giant steps. Using the diaries, reminiscences, and letters of 103 women who made the westward journey with their men, she provides solid support for feminists who, since at least the 1960s, have been reminding the world that the 350,000 pioneers came from both sexes. Refreshingly, she has abandoned the silly attempt to prove that anything men can do, women can do as well--or better. Instead, she emphasizes the differences between the sexes, in their duties, experiences, and perceptions. One summary sentence in her accompanying narrative says it all: ''In this random sample of 97 diarists, 50 women traveled with 191 children and 16 were pregnant or had recently given birth on the overland journey.''

Mostly in their late teens and 20s, these women were certain that, come what might, they had to keep the family healthy, well-fed, clean, and together. One wife wrote: ''The men had a great deal of anxiety and all the care of their families, but still the mothers had the families directly in their hands and were with them all the time.'' The daily routine included baking; washing; cooking; child care; scrounging for berries, herbs, and roots; pitching tents; incessant packing and unpacking; and visiting the sick.

Interestingly, although the diarists frequently described being frightened by Indians, the women also perceived them as helpful guides who gave excellent directions, advice, and needed services. Thus one woman tempered her ''fear of the red enemy'' with her observation that Indians were ''generally friendly.''

Beginning their trek in the spring of the year, emigrants traveling in large wagon trains would be constantly on the move for six to eight months, rushing to cover the 2,400 miles over plain, desert, and mountains before the snows. No longer did they have the luxury of observing the Sabbath, instead substituting Bible-reading during Sunday dinner. Even childbirth was no reason for slowing down. One diarist commented that following delivery, three women ''traveled right along the next day, mothers and babes with the rest of us.''

In addition to well-placed quotations interspersed in her narrative and extensive excerpts from four diaries, Professor Schlissel has included 48 photographs that magnificently illustrate the text.

Amid all these riches, however, the editing is disappointing. For example, there are egregious misspellings--''supercede'' for ''supersede'' --and an annoying carelessness with numbers as in ''two hundred thousand workers'' in New York in 1839, when that city's entire population of men, women, and children in 1840 was 312,000. Unhappily, these are only two among too many errors. Surely, however, these mistakes can be corrected in future editions--of which there should be many.