Two companies charged with corrupting the bidding process for a $24-million San Diego County telephone system contract pleaded no contest to fraud and racketeering charges. County supervisors canceled the contract in 1983, after allegations surfaced that the pact was tainted by kickbacks, bribery and other irregularities. By entering the pleas to 48 criminal counts in federal court, the telephone contractor, Telink Inc. of Anaheim, and its parent company, Burnup & Sims Inc., culminated a year of plea-bargain discussions that followed a two-year grand jury investigation. Telink, which is no longer in business, pleaded no contest to 44 felony counts. Burnup & Sims of Plantation, Fla., pleaded no contest to four counts. Burnup & Sims will pay $1 million in fines and penalties and $3.5 million in restitution to the county. The county will keep $2.4 million worth of telephone equipment.