American Finance System, Inc., a Silver Spring consumer finance company, reported an increase in third-quarter profits to $1.3 million (23 cents a share) compared with operating earnings of $915,000 (15 cents) in the same period last year.

Revenues were up slightly to $21.37 million from $21.3 million, AFS said yesterday. In the 1977 period, there was a tax loss carryforward benefit that raised final net income to $1.3 million (23 cents).

In the first nine months this year, AFS earned $3.7 million (64 cents) vs. operating profits of $3.9 million (73 cents); tax loss benefits in the nine months of 1977 brought net income to $5.4 million ($1.07). Revenues increased to $65 million from $63 million.

Capital Mortgage Investments, a real estate investment trust based in Chevy Chase, reported a significant reduction in losses for the quarter and nine months ended Sept. 30.

The third-quarter loss was $12,000, after a one-time gain of $323,000 from selling assets and an addition of $450,000 to reserves for possible loan losses. A year earlier, CMI lost $3 million.

In the first nine months, the trust lost $123,000 after adjustments for extraordinary items compared with a net loss in the 1977 period of $3.6 million.

Vice president John Wolf said banks participating in a $32 million credit agreement have approved an amendment, reducing from three percent to one percent, the interest rate on outstanding debts from Aug. 1 through Dec. 31. The amendment cures a default resulting from failure to pay the higher rate.