"This is our last chance," said Roger Bomsta, shutting the door of a cream-colored 1981 Plymouth Reliant station wagon, one of the first in a line of new, compact K cars that Chrysler Corp. will begin selling in about three weeks.

The door closed with a firm, reassuring snap, a hopeful omen for a car line that spells the difference between bankruptcy and deliverance for Chrysler.

The first production K cars from Chrysler's Newark assembly line were driven away today at a ceremony attended by the top officials of Chrysler and the United auto Workers, and the state and federal officials who lobbied sucessfully to win government-backed loans for Chrysler.

Several hundred of the Newark plant's 4,000 workers were also on hand -- including Bomstra, a quality assurance manager, who says he has spent hours at the Baltimore depots where foreign cars are unloaded, checking the quality of the competition. This time, Chrysler can compete, he says.

It will be another month before the public gets a chance to begin voting on that question, but no doubts about the outcome were expressed today.

Speaker after speaker declared that Chrysler's K cars -- the Plymouth Reliant and Dodge Aries -- have become not just a symbol of Chrysler's fate but also of America's ability to match the technical expertise of Japanese automakers.

At times, today's ceremony souded like a Remember Pearl Harber Rally. Lee A. Iacocca, Chrysler's chairman, promised his company will "teach those Japanese a lesson they'll never forget."

Douglas Fraser, president of the United Auto Workers, said the idea that Americans can't build cars as well as Japan is "an absolute slander to the American worker."

Sen. William V. Roth Jr. (R-Del.) called for five years of import protection against Japan to permit American producers to recover. But he was no match, rhetorically, for Sen. Joseph R. Biden Jr. (D-Del.), who said that with the Chrysler crisis American industry labor and government found themselves at the "edge of the precipice."

"We all understand how far down that is" he said warning that Japanese automakers stood ready to push them in. The K cars will "drive the Japanese back to Japan and other parts of the market," he promised.

In fact, the K cars are much more of a threat to the intermediate-sized compacts made by Ford Motor Co. and General Motors Corp., acknowledged Gar Laux, Chrysler's executive vice president for sales and marketing.

Chrysler is confident, he says that it can rebuild its share of the U.S. market to 12 percent or 13 percent, where it stood before the slump a year ago that brought the company close to insolvency.

Chrysler lost 499 dealers in the first seven months of the year, leaving just under 4,000. But 43 new dealers were recruited in July and that figure may be matched in August, Laux said.

The dealers will get, on the average, about 10 k cars each this month -- all that Chrysler's two K-car production plants can put out in September. Production at a Detroit plant began last month. The new cars represent immediate cash to Chrysler, which has lost $2.1 billion since January 1979. As soon as the cars leave the plants, Chrysler will bill the dealers.

The introduction of its new line has left Chrysler executives sounding increasingly optimistic. Jerry Greenwald, Chrysler's financial vice president, said the company may not need to draw on $200 million more from the $1.5 billion in federally guaranteed loans approved by Congress in December. It already has drawn $800 million and was expected to ask for the next installment soon. Company officials have even begun predicting a fourth-quarter profit.

That depends, however, on the public's accptance of the new cars, which in turn rests on the quality question, Iacocca said today.

Chrysler cleaned out its Newark plant, built originally to manufacture tanks for the U.S. Army, and invested $50 million in new automated robot welding machines, computer-operated quality-control monitors and other assembly line equipment.

It has entered into an agreement with the United Auto Workers to establish quality action teams at production plants to review construction and design problems and has stepped up auditing at some 70 critical points on the asembly line.

Its auto assembly plants still will not be confused with heaven on earth -- workers mentioned the oppressive heat inside the plant during the recent 100-degree weather. But, says Al Mancari, electrical repariman and 28-year-Chrysler veteran, the attitude in the plant is different. "Everbody's working together the supervisors the men. You've got 100 percent." Management attitudes have changed as well, he and other employes said. "If we find any trouble, we can stop the line. Before we couldn't. We won't let the cars get out with a problem. It's our bread and butter."

The struggle to save Chrysler has triggered the competitive instincts of the auto workers says Fraser, the union president. "TheyRe being maligned, and they want to do something about it," he said.

History suggests that the first batch of K cars will be eagerly snapped up.

The test will come next winter, when the initial owners render their verdicts on quality and performance.

"It's the cars themselves that have to live up to their reputation for quality and fuel economy," said Iacocca.