The Fairfax County supervisors, seeking to avoid a bond issue so large they feared it would be politically unpalatable to voters in the fall, yesterday rejected bids to add more road construction projects to the $134.4 million proposal.

The board voted unanimously to send the bond package, the largest ever proposed in the county, to a public hearing scheduled for July 29.

No projects were added to the bond package, which was drawn up by county transportation officials during the last several months.

The bond package includes funds to build two segments of the cross-county Springfield Bypass, as well as another 12 road building and widening projects designed to ease the severe traffic congestion that thousands of Fairfax commuters face daily.

The vote came after Supervisor Audrey Moore (D-Annandale) asked for estimates on other projects she wants included in the referendum.

Moore insisted that the extra projects would not improve traffic for commuters heading east into the District or Arlington for work. She said most of the road proposals in the bond package helped north-south traffic in the county at the expense of east-west traffic.

"If you're going to open this thing up," said Supervisor Nancy K. Falck (R-Dranesville), "there isn't one of us that doesn't have six, seven, eight projects we'd like to add. We all have problems in our districts."

"All of us are swallowing a little hard here," said Board Vice Chairman Martha V. Pennino, a Democrat who said she found it difficult to support the package because it does not include any improvements on Reston Avenue in her Centreville District.

Fairfax politicians are fond of saying that the county needs more than $1 billion to solve all its road problems, and officials acknowledge that the bond package will ease, but by no means solve, countywide traffic problems.

But supervisors would not support Moore's attempt to add to the package, saying they feared voters would look askance at a road-bond referendum that would allow the county to borrow much more than the $134.4 million in the current proposal.

The board is expected to cast a final vote Aug. 5 to place the bond referendum on the ballot Nov. 5.

County Board Chairman John F. Herrity, a Republican, stressed that about 50 percent of the workers in Fairfax live and hold jobs in the county. By 1990, he said, the figure should increase to about 60 percent. "The bypass recognizes the need of people to move across this county," he said.

The bond package calls for building two segments, totaling about eight miles, of the planned 35-mile bypass that would sweep from Leesburg Pike (Rte. 7) in the north of Fairfax to Rte. 1 in the south.

Of the two segments that would be built from funds raised in the proposed bond issue, one would connect the Dulles Toll Road with Rte. 50 in the county's northwest, and the other would run from Rolling Road across Interstate 95 to Beulah Street in the south of the county. The two bypass segments account for about $90 million of the bond package.

Of the 12 other projects, about a third call for widening or building roads in the county's Lee District, just south of Alexandria. Lee District contains some of the oldest neighborhoods in Fairfax County.