An Unprecedented coalition of local religious leaders has issued a call to use the Thanksgiving season as a time to strengthen family ties.

The statement, signed by seven Roman Catholic, Protestant and Jewish leaders, calls attention to the designation of this week by Congress and President Carter as National Family Week.

"We welcome this formal recognition of the vital role of the family to the stability and happiness of society and call upon all citizens in the Greater Washington, D.C. area to observe the week with appropriate activities to strengthen and enrich their families," the churchmen said.

The statement also urged families "to reach out to those who may be alone during this holiday season and invite them to share in your love."

Signing the statement were Cardinal William Baum, Episcopal Bishop John T. Walker, Rabbi Stanley Rabinowitz of Adas Israel Congregation, and L. Ralph Mecham, president of the Washington Stake of the Church of Jesus Christ of Latter-day Saints.

Also, the Rev. B. J. Moffett, state overseer of the Church of God; the Rev. Edward White, of the National Capital Union Presbytery, and Robert H. Pierson, retiring international president of the General Conference of the Seventh-Day Adventist Church.

Initiative for the statement came from Mecham, who cleared the proposal with international Mormon headquarters in Salt Lake City. "It is unusual for us to go in on these things," a Mormon spokesman here acknowledged. He added: "We felt so strongly the importance of anything to strengthen family ties that we decided to do it."

Like Mormons, Seventh-Day Adventists do not participate extensively in interfaith endeavors.