Internation Bank of Washington doubled its net income for the third quarter, and its earnings for the first nine months surpassed the company's best full-year figures.

The Rouse Co. of Columbia turned in a 30 percent gain in profits for the third quarter in another earnings report made yesterday.

International Bank earned $4.9 million (67 cents a share) in the third quarter, up from $2.4 million (33 cents) for the same period a year earlier.

Revenues increased 73 percent, from $3.8 million to $6.5 million, for the Washington merchant banking company, which owns interests in insurance, manufacturing, finance, foreign banking and leasing companies throughout the world.

For the first nine months of its fiscal year, IB earnings increased 45 percent to $12.5 million ($1.74) from $8.6 million ($1.21). During fiscal 1977, its best year ever. IB earned $1.30 a share; analysts had predicted earnings of about $2 this year, a figure that was termed "conservative" after yesterday's report.

Chairman George Olmsted noted that International Bank's stockholder equity passed the $100 million mark as a result of third-quarter gains.

Rouse reported earnings of $2.7 million for the three months ended Sept. 30, up 30 percent from the $2.08 million earned in the same period a year ago.

The big shopping center and real estate developer earned just over $7 million for the nine months of its fiscal year, up from $6.1 million last year.

Rouse reports its earning before noncash charges and before gains on sales of property, and does not provide per-share earning figures.

The company reported strong performance from its mortgage banking division and from its retail centers, including the Village of Cross Keys in Baltimore.