More of the Washington area's biggest banks weighed in with reports of declining profits yesterday, blaming increased problems in their real estate loan portfolios.

Sovran Financial Corp., Signet Banking Corp. and Crestar Financial Corp., the holding companies for the area's second-, third- and fourth-largest banks, said they would each boost cash reserves to protect against potential losses from real estate lending, causing significant declines in second-quarter earnings.

The round of announcements comes one day after MNC Financial Inc., the area's biggest bank holding company, announced that it would lose $75 million in the second quarter, the largest loss yet attributed to the weak commercial real estate market and tougher oversight of banks by federal regulators.

Signet said its profit plummeted 90 percent in the second quarter, to $2.9 million (11 cents a share) from $31.3 million ($1.15) in the same period last year.

Crestar fared a little better in the quarter, with profit dipping 64.5 percent, to $9 million (26 cents) from $25.4 million (81 cents) earned in the same quarter last year. The company said its decision to boost cash reserves by $25 million in the quarter had a significant impact on its bottom line.

Sovran, meanwhile, said it expects a similar decline when it reports final results for the quarter next week. The company said it expects earnings per share to drop 66 percent, to about 37 cents from $1.10 earned in the same quarter last year. Sovran Chairman Albert B. Gornto said the results follow an examination of the bank's real estate loans by federal regulators.

Although the Dow Jones industrial average yesterday topped 3000 points for the first time, local bank stocks remained in the doldrums, battered as they have been all year by investor fears of the health of the region's commercial real estate market.

Sovran's stock remained unchanged at $26.25; Signet also remained steady at $18.75; and Crestar, with earnings slightly better than the rest, showed a modest gain of 50 cents to close at $21.37 1/2.

"To finally have the news out on some of these banks is great, but it's nothing we didn't expect," said Anthony Davis, bank analyst for Richmond-based Wheat First Securities.

Davis said he first entered the quarter hoping he would see some evidence of stability in the real estate market, "but we just haven't found that. It's clear now that it's not a good market and it's probably not going to be for a little while."

Davis and other analysts said they are reluctant to predict an end to the financial turmoil, saying conditions in the real estate market will continue to dictate bank earnings for the next several quarters.

"Until the market turns, it's anybody's guess," Davis said. "Some banks might be cutting themselves some slack but taking big hits now, but future earnings will simply depend on the market."

Nonperforming loans -- those loans to businesses that are not being paid on time -- increased sharply at all three banks.

Signet's nonperforming loans reached $148.7 million in the quarter, more than double the level of nonperforming assets in the second quarter last year.

Crestar said its nonperforming assets totaled $119.1 million in the quarter, compared with $58.3 million in the same period in 1989. Crestar attributed the increase to weaknesses in the regional real estate markets and said it expects the trend to continue through the remainder of 1990.

Sovran also said it expects nonperforming loans to increase by $120 million in the quarter, to about $250 million. The company broke down its troubled assets geographically as follows: $18 million from Maryland, $75 million from Virginia, $6 million from the District and $21 million from Tennessee.

To cover the potential weaknesses in their real estate portfolios, all three institutions announced significant increases in their loan loss reserves, the financial cushion that protects against possible loan defaults.

Signet boosted its reserves to $120 million, up 38 percent over the same quarter last year; Sovran increased its reserves to $265 million, up 37 percent over the second quarter of 1989; and Crestar boosted its reserves to $121.6 million, up 33 percent over the same period a year ago.

For the first half of the year, Signet said it earned $30.1 million ($1.13), compared with a profit of $62.8 million ($2.29) it earned in the first half of 1989. For the first six months of the year, Crestar reported a profit of $36.1 million ($1.11), compared with $49.8 million ($1.59) earned in the first half of 1989.

In addition to the banks' troubles, three area thrifts also have reported problems in their loan portfolios.

United Savings Bank, which operates 15 branches in Northern Virginia, said it anticipates a substantial increase to its loan loss reserves for the quarter because of a rise in problem loans to $50.4 million. The company said the level of problem loans "raises serious doubt that United can achieve profitability and meet regulatory capital requirements."

Piedmont Federal Corp., which has branches in Prince William and Loudoun counties, said it also expects to boost its reserves because of a rise in problem loans. The Manassas-based company said the increase likely will result in "a substantial loss for the quarter and the year."

Meritor Savings Bank, which has offices throughout Maryland and the District, reported a second quarter loss of about $138 million because of a drive to shrink assets and improve capital, the Philadelphia-based company said. In addition to the restructuring, the company's bottom line was hurt by a $35 million addition to its loan loss reserves, and establishing a $54 million reserve against gains that had been anticipated but are no longer likely.