Five women, two of them established nuns and the other three postulants, began a new religious congregation to be known as Our Lady's Missionaries of the Eucharist in Falls Church this week.

The new Roman Catholic community, which was launched Sunday as a Vatican approved "pious union" by Bishop Thomas J. Welsh of Arlington, will be devoted to renewing the devotional life of lay men and women. Their efforts will focus on devotion to the eucharist and to the Virgin Mary.

For the first year of the community's existence, according to a diocesan spokesman, the women will spend only one or two days a week with lay persons, leading public devotions based on the "Liturgy of the Hours."

The rest of the time they will spend in study and prayer and the formation of their own religious life as a community.

The focus of both public and private devotion is the fixed schedule of daily Scriptures, prayers and meditations - one for every day of the year - that used to be known in the church as the holy office, for use by priests and others who have taken religious vows.

With the changes of recent decades, these devotional exercises have been adapted by the church and promoted for use among lay persons as well as those within holy orders.

Each twice-a-day exercise may include a hymn, a psalm, other Scripture, meditations on the life of the saint of the day and intercessory prayer. It is "a conversation between God and man," according to an explanation offered in the compendium of these exercises, "Christian Prayer: The Liturgy of the Hours."

The newly formed congregation is headed by Sister Joan Noreen, who last, year inaugurated a Liturgy of the Hours program for the National Shrine of the Immaculate Conception.

The women have taken over a private residence at 6419 Shady Lane in Falls Church as their convent.