The Better Business Bureau has taken the unusual step of publicly criticizing the advertising practices of many Washington area automobile dealers, noting such problems as false indications of discounts and financing.

In a strongly worded memo mailed to about 140 new car dealers, Douglas W. Tindal, president of the Metropolitan Washington Better Business Bureau, said his organization has reviewed local auto advertising over the past several months and found "serious problems relating to the accuracy and believability of many of these ads."

"For the last five months we have noticed that the ads have gotten worse," he said. "One breaks the rules and another does it and then it hits bottom. You can almost go through every ad in the paper and find something wrong with it. We are talking new car dealers, foreign and domestic."

The bureau's memo, which has been endorsed by the local car dealers' trade association, listed 11 examples of problems that have appeared recently in newspaper ads. It asked that "any offending dealerships take immediate action to correct them." The memo cited problems in trade-ins, freight charges and leasing deals. They include:

* Advertising "base price" automobiles when there are no vehicles available at the "base price," because most vehicles come with extras which can raise and sometimes double the advertised "base price."

* Advertising a sale price in conjunction with a low monthly payment, then in fine print disclosing that the advertised monthly payment is for a leased car rather than a purchase.

* Offering "six percent" financing with a difficult-to-read disclaimer. The bureau said six percent financing was not available and that this particular ad appeared to violate the Truth-in-Lending law.

Tindal said the bureau routinely monitors advertising "for truth and integrity" and then tries privately to persuade offending businesses to voluntarily improve their ads.

But recent bureau efforts to get individual new car dealers here to change their advertising ways have failed, Tindal said yesterday. "We have contacted 25 or 30 dealers, through the mail, and we have had meetings with one dealer who has a number of agencies, and we haven't been successful in having the ads look the way we think they should."

For that reason the bureau decided to go public with its concerns, he said.

"Normally we wouldn't send out a press release," Tindal said. "But we are doing it this time hoping that the glare of publicity will make dealers react more positively."

In addition, the bureau met last week with the board of directors of the Automotive Trade Association, National Capital Area, a local trade group that represents about 90 percent of the area's new car dealers. Association chairman Morton Zetlin, an Arlington dealer, said yesterday that the board endorsed the bureau's effort to improve the quality of local auto advertising and that the list of points in the bureau's memo would help dealers upgrade ads.

However, Zetlin said the "problem that auto dealers have is when someone else advertises an attractive gimmick, they have to be competitive; they have to run ads that will bring people into their showrooms."

Zetlin said that "if a newspaper such as The Washington Post feels an advertisement is inaccurate or misleading" they should not accept the ad.

Dealers themselves are responsible for their ads, Post advertising officials said. "If something is submitted that we think contains a misleading statement, we will bring it to the attention of the dealer," said Scotte Manns, director of advertising sales, "but the Post is not an enforcing agency."

Local consumer officials familiar with auto advertising said the car ads have become so misleading that it is almost impossible for consumers to obtain from them a clear understanding of what they must pay for a new car.

George Rose, head of the auto complaint section in the Montgomery County Office of Consumer Affairs, said car ads feature low prices because "If dealers advertised the price that new cars really sell for, who would go in to buy? Very few.

Dealers use "gimmick headlines in advertisements to attract and get customers into their showrooms, where they count on their sales ability to sell you the car," he said.

Rose said that 32 of the 43 Montgomery County dealers now subscribe to a code of ethics started last May by the county's consumer office in an effort to reduce consumer complaints about car dealers. Dealers who subscribe to the code, which is unique, agree to comply with some of the toughest consumer laws and advertising standards in the nation. In exchange, they receive the county's advertising seal of approval, which can be used in their advertising as a way to let consumers know that they abide by the county code.