Criterion Insurance Co., an automobile insurer affiliated with Government Employees Insurance Co., yesterday reported a sharp increase in profits during 1977.

Net income was $8.4 million ($5.73 a share) compared with $4 million ($2.74) in 1976, reflecting a profit of $3.4 million from underwriting insurance premiums last year. In 1976, Criterion had an underwriting loss of $8.3 million.

The 1977 results include utilization of tax loss benefits from 1975 and 1976; excluding the extraordinary gains, Criterion profits in 1977 would have been $5.6 million ($3.84 a share). Premium volume last year was about $70 million compared with $64 million in 1976.

In the fourth quarter alone, Criterion earned $1.6 million compared with $113,000 in the same three months of 1976. At year's end, the firm had 174,000 policies in force, one percent more than in 1976.

Company officers said the number of claims reported in 1977 fell by 19 percent. "As our policies-in-force count was relatively stable during the year, the drop in the number of claims reported reflects continued improvement in claim frequency and policyholder selection during 1977," said Chairman Alvin E. Kraus and President George F. Lewin . . .

Capital Mortgage Investments, a real estate investment trust in Chevy Chase, reported profits of $190,354 (11 cents a share) in the final quarter of 1977 compared with a loss of $1.3 million a year earlier. However, CMI said the net income reflected an extraordinary gain of $817,000. Without it, CMI had an operating loss of $626,000.

For the full year, CMI lost $3.45 million compared with a 1976 loss of $1.14 million.

Since the start of 1977, debts to bank creditors have been cut by about $34 million through cash payments and exchanging $21.3 million in assets to the banks, the trust said. By Dec. 31, nonearning investments represented 51 percent of CMI's portfolio.

Washington Real Estate Investment Trust, meantime, reported fourth-quarter profits of $730,000 (48 cents a share) compared with $586,000 (40 cents) a year earlier. For the full year, the real estate trust earned $2.5 million ($1.66) from operations compared with $2.4 million ($1.64).

A capital gain of $1.6 million last year made final net income for WRIT $4.1 million ($2.74 a share). Revenues for the trust rose to $8.7 million from $8.2 million.