NEW YORK, JUNE 16 -- Manufacturers Hanover Corp. added $1.7 billion and Bankers Trust New York Corp. added $700 million today to their reserves for potentially bad foreign loans, joining the growing number of banks taking the step.

Manufacturers Hanover, the nation's sixth-largest bank holding company, said the reserve addition would give it a second-quarter loss of about $1.4 billion and an annual loss this year of about $1.05 billion.

Bankers Trust, the nation's eighth-largest bank holding company, said it would lose about $570 million in the second quarter, and $150 million to $200 million for the full year.

Officials for both companies said they are increasing their reserves because of Brazil's recent decision to suspend interest payments on some of its foreign loans and because of the shaky economies of other Third World nations.

They also said the action was taken in light of similar moves by other major banks.

Last month, Citicorp became the first banking company to make a major addition to its loan loss reserve, announcing a $3 billion increase. Chase Manhattan Corp., Chemical New York Corp., First Interstate Corp. and others followed suit. Analysts had speculated that troubled institutions such as BankAmerica Corp. might be unwilling to take another big loss to bolster reserves.

BankAmerica lost $855 million in its last two fiscal years, and had hoped to return to operating profitability this year as a result of asset sales and heavy cost-cutting.

After Citicorp boosted its reserves, BankAmerica maintained that its own reserves were adequate. However, the San Francisco-based company last week added $1.1 billion to reserves and said it expected a $1 billion second quarter loss as a result.

The $1.7 billion addition increased Manufacturers Hanover's reserve to $2.7 billion, or about 4.9 percent of its total loans. The figure also represents 77 percent of all nonperforming loans, the company said.

At Bankers Trust, the $700 million addition boosted its reserve to about $1.3 billion, or about 4.9 percent of its total loans. The figure amounted to 100 percent of nonperforming loans, said Thomas Parisi, a Bankers Trust spokesman.

Bankers Trust said its total reserve for bad loans amounted to about 25 percent of its about $4 billion in restructured loans to developing nations.

Manufacturers Hanover's $7.5 billion Third World loan portfolio is one of the biggest among U.S. banks, and includes $2.32 billion in loans to Brazil, $1.9 billion to Mexico and $1 billion to Venezuela.

The banks have said they do not plan to use all of the additions to write off foreign loans as uncollectible. But the huge additions are seen as admissions by the banks that billions of dollars in loans may not be collected or will have to be disposed of at a loss.

Such losses can be written off against the reserve instead of against current earnings, which in effect cushions the banks from future unexpected shocks stemming from foreign loans.

Manufacturers Hanover said $1.85 billion of its reserve was allocated to cover loans to 31 countries.

In estimating its second-quarter loss, the firm said it expected a tax credit of $300 million and a gain of $50 million from the sale of assets. It plans to gain $200 million to $300 million from the sale of other "undervalued assets" on its books over the next few years.

Manufacturers Hanover also said that because it is taking the step now, its future earnings would not be burdened by additions to its loan reserve.

Like other banks that have taken the step, Manufacturers Hanover and Bankers Trust indicated they would continue their current dividend policies.

Bankers Trust said it expects to realize a 1987 tax benefit of about $60 million to $70 million from the loss.