A plan to merge four inner city Roman Catholic high schools for girls into one was both assailed as an abandonment of blacks and alternatively praised as far-sighted planning in a three-hour open hearing yesterday conducted by the archdiocesan school board.

Under discussion was a proposal to close St. Cecilia's Academy at 601 East Capitol St., St. Patrick's Academy at 924 G St. NW, and Immaculate Conception Academy at 2408 K St. NW. Money gained from selling the three properties would be used to expand St. Anthony's School at 1001 Lawrence St. NE to accommodate 850 girls -- the estimated size of the combined enrollment of the four schools.

The archdiocese maintains that the merger, which, if approved would become effective in September 1981, is necessary because of rising costs, deterioration of the buildings at St. Patrick's and Immaculate Conception, and declining parochial school enrollments.

More than 150 persons attended yesterday's hearing and 33 of them -- parents, priests, teachers, lay leaders and several students -- offered their reactions to the plan.

Some of the sharpest criticism came from Sister Helen Therese, who read a statement representing the views of the Secretariat for Black Catholics. The position of the Secretariat is considered sirnificant since the enrollment of the four schools is overwhelmingly black.

"The Secretariat for Black Catholics rejects the proposal as given," said Sister Therese. She charged that "the primary accent about consolidation has been financial" with statistics and tables "quoted enthusiastically in a frenzy to convince the public of the dilemma."

"Little weight," she continued, "has been given to the church's commitment to the poor and middle class of the inner city whose Catholic secondary schools are being phased out."

She said the black Secretariat proposed as an alternative the merger of St. Patrick's and Immaculate Conception with an expanded St. Cecilia's. Several others, including a representative of the St. Cecilia's faculty, supported this proposal.

When a board member reminded Sister Therese that the church "must face up to reality when we are dealing with a financial crises, she retorted, "I really feel the problem here comes from a lack of commitment... the people's interest is not considered."

In her testimony, Sister Noretta, principal of St. Anthony's, said the board's merger proposal did not represent the church's "withdrawal from education of blacks." She said it was a move "to strengthen, not weaken education in the city."

Priests from both St. Patrick's and St. Stephen's the parish church of Immaculate Conception, also testified at the hearing. Both indicated the schools no longer serve their parishes, since few families with school-age children now are members of the parish.

Msgr. Edward Spiers of Catholic University, who is a consultant to the Catholic school board, had the last word yesterday. He called the merger proposal "a bold step forward, not a retreat; an expansion of educational opportunity for girls, not a reduction."

The final decision on the proposal rests with Cardinal William W. Baum. Neither the cardinal nor his auxiliary bishops was present at yesterday's hearing.