Safeway Stores Inc., North America's largest food retailer, reported yesterday that its second-quarter net income dropped by 32 percent to $25.5 million (98 cents a share) from $37.7 million ($1.44) a year ago.

Sales in the quarter were $3.78 billion, up from $3.35 billion.

The lower second-quarter earnings "reflect an increased competitive posture" on the part of the company, it said.

First-half net income dropped to $46.1 million ($1.77 a share) from $50.2 million ($1.92) in the first half of 1980 as sales rose 11 1/2 percent to $7.37 billion.

Hurt by lower operating earnings at its National Broadcasting Co. and Hertz Corp. subsidiaries, RCA Corp. reported a 24 percent decline in second-quarter profits to $58.4 million (55 cents a share) from $77.1 million (80 cents) as sales dipped to $1.957 billion from $1.964 billion.

RCA said that total NBC profits were up because the 1980 second quarter included a $33.7 million pretax loss resulting from the cancellation of NBC's plans to televise the 1980 summer Olympics in Moscow.

First-half profits were $100.3 million (88 cents), down 36 percent from $155.8 million ($1.69). Sales were $3.90 billion, down from $3.93 billion.

Allied Corp. reported that earnings surged to $87 million in the second quarter, up 19 percent from the same 1980 period and a record for any quarter in the history of the diversified company.

Second-quarter earnings come to $2.40 a share on record revenues of $1.59 billion, compared with earnings of $73 million ($2.02 a share) on revenues of $1.36 billion in the same period a year ago.

First-half earnings totaled a record $171 million ($4.73) on revenues of $3.16 billion compared with profits of $141 million ($4.08) on sales of $2.75 billion in the first half of 1980.