Tests of concrete beams that support four elevated walkways in the D.C. government's new municipal center at 14th and U streets NW indicate that the walkways are structurally safe, according to McLaughlin Construction Management Inc., which is supervising the construction.

The beams cracked during construction, raising fears that the walkways might collapse. Workers reinforced the beams in December 1984, but an official of Sherman R. Smoot Corp. of Washington, which poured the concrete on the job, wrote to McLaughlin in July that the firm still saw "a serious problem at hand."

Following a press report, McLaughlin tested the strength of the beams three times, according to Dick Janec, the firm's project executive. Janec said temporary supports under the beams were removed and the cracks were measured to see if they had widened. He said workers also checked for excessive movement of the beams.

Janec said Richard T. Ball, the main structural engineer for the project, told McLaughlin, "The readings are well within the acceptable range," indicating that the beams would support their loads.

The mayor's office Friday obtained a $5.2 million increase in the construction budget for the building, which has been dogged by various construction problems and delays.

D.C. City Council member Nadine P. Winter (D-Ward 6), chairman of the council's Public Works Committee, filed a formal disapproval of the mayor's request for the extra money, which will increase the total cost to $41.7 million. However, Winter did not bring up her disapproval action before the full council by the deadline Friday, and the increase was approved automatically.

Winter said, "It seems to be the consensus of my colleagues that we've gone this far, we have to complete it, there's no choice."

She said she had given the Public Works Department "a mandate" to complete the project within 90 days. The project is a year behind schedule.