Union Trust Bancorp, which includes the $969 million deposit Union Trust Company of Maryland, reported that first-quarter earnings for 1981 climbed to $2.58 million ($1.05 a share) before security losses from comparable earnings of $1.806 million (74 cents) in the same quarter a year ago.

Bank officials attributed the improved performance to a better balance of interest-sensitive assets and liabilities, tighter expense control and satisfactory core deposit growth. Per-share earnings after security losses were 93 cents per share, up 27.3 percent from 73 cents a year earlier.

Average assets of Union Trust in the first quarter were $1.266 billion compared with $1.231 billion in the same period in 1980. Average deposits were up 5.9 percent to $934 million, and net loans were up 1.6 percent to $809 million.

Petroleum & Resources Corporation reported new assets of $279.819 million as of March 31, compared with $204.566 million in 1980. That equals net assets of $42.87 per share after capital gains distribution of $14.927 million, or $2.48 per share, in February 1981 and with $5.095 million $1.75 convertible preferred stock outstanding, compared with $32.88 a year earlier.