The Arlington County Board is scheduled to decide Saturday whether to place five bond referenda totaling $49.2 million on the November ballot for such projects as water distribution and street improvements, park acquisitions, neighborhood conservation programs and Metrorail construction.

County Manager Larry J. Brown proposed the potential bond package, which he said county officials hope will be the last bond referenda put before voters in an odd year. County officials decided a few years ago, he said, that such referenda preferably should be on the ballot only in even years when there is a larger voter turnout because of national elections.

"It seems fairer," said Board Chairman Ellen M. Bozman, "to have the bonds on the ballot the year most people come out to vote and can express themselves on them."

The board could accept or reject any of the proposed referenda during Saturday's deliberations, which are expected to focus primarily on a proposed $40-million Metrorail bond issue and whether to ask for a $1 million parks and recreation referendum.

The Metrorail bond issue is expected to be the most controversial and would represent a major portion of what is expected to be the county's capital obligations through 1988 toward construction of the 101-mile subway system.

Metro officials currently compute Arlington's financial obligation to be $64.3 million. After anticipated state and federal aid over the next five years is deducted, Arlington would still owe $11.4 million if the referendum is passed. A special citizens' advisory committee has recommended that the remainder be drawn from pay-as-you-go capital or additional state aid. By current projections, the county's capital contributions toward the construction of the subway system will end in 1990.

The citizens' committee, which includes both former Republican and Democratic County Board chairmen, has recommended that there be one $40-million bond referendum. But Chairman Bozman said the County Board may want to consider splitting the amount into a $20-million referendum this year and again next year.

A Metrorail bond referendum in 1975 was turned down by voters, as were all bond referenda that year. "It was a bad year for bond referenda," Bozman said. "Afterwards, people came up to me and said they voted against it, saying, 'I don't know what it's going to buy, what the system will be, what it will cost.' So I don't want to go back to the voters until we know specifically what we're after."

The proposed $1 million for parks and recreation would allow the county to continue purchasing small parks and open spaces throughout the county. While no specific properties have been identified, the county manager has suggested they could include land in the Rosslyn-Ballston Metro corridor.

Bozman speculated the board may not approve such a referendum. "We are almost totally out of park purchasing money," she said. "This is an area we are most concerned about keeping at a reasonable level . . . . I think people perceive it as a non-requirement, that it's nice to have parks, but more important to have sewers."

Brown has proposed a $3.1 million for improvements to the water distribution system. These funds, he said, would improve overall operations, increase firefighting capabilities, promote economic development and meet county obligations to site development plans.

Also proposed is $3.1 million for streets and highway improvements, specifically the repaving of primary and secondary streets where the surface has deteriorated. The proposal includes $677,000 for improvements to Arlington Ridge Road, where the county is conducting a test on the effects of narrowing the road from four to two lanes, as citizens have requested. Another $500,000 has been suggested for improvements to S. Walter Reed Drive, from the county line to S. Wakefield Street.

The proposed bond package also provides for $2 million for residential and commercial conservation projects. These funds, usually matched by private funds in the neighborhood, generally are used for improvements in roadways, curbs, gutters, pedestrian ways, storm drainage and neighborhood landscaping.

Business projects, which could be earmarked out of the funds, Brown suggested, include improvements to Columbia Pike and in the Shirlington area where WETA plans to consolidate its public radio and television station operations.