In November, top U.S. auto safety officials made an unusual request of Transportation Secretary

RELATED ARTICLES Tax needs may undo US online bet ban Sales growth for Boeing shifts to civilian side A move to tighten controls on painkillers Tobacco loses its place in US health efforts RBI raises key rates; may turn auto, home loans expensive

Ray LaHood. After reviewing complaints about Toyota vehicles, the regulators said they believed the automaker was stalling their inquiries and wanted to go to Japan to stress just how serious their concerns had become.

Executives at Toyota ‘‘were dragging things out, and we’d had it,’’ a senior U.S. transportation official said in recounting new details of the talks. ‘‘We were getting excuses that didn’t make sense anymore.’’ Mr. LaHood approved the unprecedented trip, but it would be a month before his top safety aides met with Toyota executives and another month before Toyota told Washington that it had found problems with some accelerators.

Not once in more than six years of U.S. reviews of Toyota’s problems did officials at the National Highway Traffic Safety Administration, which regulates automakers, use their power to subpoena Toyota’s records, even though they said they believed the automaker was withholding critical information.

Now, with the recalls of about eight million Toyota vehicles since late last year, including more than 400,000 of the 2010 Prius and other hybrid models this week, the U.S. traffic safety agency is likely to be scrutinized as much as Toyota itself. Members of Congress, independent auto experts and others say they want to know why the agency did not act more aggressively in investigating Toyota’s problems.

‘‘This is the most extensive vehicle recall in history, and we want to know, what did Toyota know about its defects and when did they knowit, and what did N.H.T.S.A. know and did it act quickly enough?’’ Representative Henry A.

Waxman, the California Democrat who leads the House Energy and Commerce Committee, said Tuesday.

Some congressional officials and outside experts say they believe the safety agency has become too close to the industry it is charged with regulating, as a number of former agency employees have gone to work for Toyota. Among other issues that need to be addressed, they also cite the agency’s limited use of fines or subpoenas against auto manufacturers, a dearth of technical expertise in areas like electronic throttle problems and frequent turnover in its leadership.

Joan Claybrook, who was the director of the agency in the Carter administration, said that it ‘‘should be the government cop on the auto regulatory beat,’’ but too often it was not.

‘‘It has enormous authority to do its job,’’ she said, ‘‘but it doesn’t always have the staff or money. And in this particular case, they took the road of least resistance.’’ Mr. Waxman’s committee has sought documents from the safety agency and has scheduled a hearing this month on the problems. A second group, the House Oversight and Government Reform Committee, postponed a hearing until Feb. 24.

In recent days, Toyota has started taking out full-page newspaper advertisements to repair its reputation and has brought on new lobbyists to make its case in Washington, where many lawmakers have benefited from the campaign contributions. And transportation officials are pushing back.

‘‘The National Highway Traffic Safety Administration has the most active defect investigation program in the world,’’ Mr. LaHood said Tuesday in a statement to The NewYork Times. ‘‘Its safety experts are dedicated to finding and fixing safety problems, and they review 30,000 consumer complaints every year. Over just the last three years, N.H.T.S.A.’s investigations have resulted in 524 recalls involving 23.5 million vehicles—astellar record.’’ But internal agency documents and interviews with auto safety experts demonstrate that the agency and the auto giant it regulated engaged in a Kabuki dance of sorts in the months and years before tensions coalesced.

Drivers filed complaints by the dozens aboutmysterious accelerations and other hazards, government regulators opened official reviews, Toyota promised answers, the regulators complained about not receiving the information they needed, and in the end, almost nothing came of any of it.

Six times after 2003, the U.S. agency opened inquiries into possible Toyota safety problems, and six times it closed them without any significant action.

In 2008, for instance, the agency examined a request from the owner of a Toyota Tacoma pickup that it investigate ‘‘sudden and uncontrolled acceleration’’ of the vehicle. After a preliminary review, the safety agency concluded in a memorandum given to House investigators: ‘‘In view of the need to allocate and prioritize N.H.T.S.A.’s limited resources to best accomplish the agency’s safety mission, the petition is denied.’’ In recent years, the agency has dealt with financing and staff cuts. The Transportation Department announced last week that the administration was seeking money for 66 new positions.

The agency also has had a revolving door of leaders, with about a half-dozen directors since 2005. The current administrator, David Strickland, was confirmed only in December.

The agency was stymied by Toyota’s centralized decision-making, but it did not act aggressively in its dealings with the company’s leaders. During its six investigations of defects, agency investigators never met with Japanese executives — only with Toyota officials in the United States.

Christopher Santucci, a manager of safety affairs for Toyota in Washington, testified in a deposition in a lawsuit that all decisions on defects and vehicle recalls had been made in Japan.

Government regulators were routinely told during investigations that requests for safety data or vehicle testing must be relayed to Japan for answers. By the autumn of last year, N.H.T.S.A. officials had become frustrated by delays in receiving information.

Even though the agency was not getting all the information it wanted from Japan, it did receive data about possible defects from State Farm, the insurance firm, beginning in 2007. The agency said that information was incorporated into its continuing investigations, but congressional officials say it should have set off louder warnings at the agency.

Congressional investigators have indicated that they are looking into the safety agency’s ability to investigate possible defects in Toyota’s computerized, electronic throttle-control systems. The agency is expected to hire outside experts to assist in its inquiry, said a federal official with knowledge of the decision.

But the Transportation Department said the move was not a sign of any shortcomings in its level of in-house expertise.

Since 1980, the agency has conducted 141 investigations into throttle controls, both mechanical and electronic versions, the department said.

The Toyota recalls occurred a decade after N.H.T.S.A. withstood heavy criticism from Congress over its failure to detect a pattern of rollovers in Ford S.U.V.’s with Firestone tires. In that case, State Farm had given the agency documentswarning of safety failures, but congressional investigators said the agency had been slowto realize the significance.

‘‘This is history repeating itself,’’ said Clarence Ditlow, who runs the Center for Auto Safety and is scheduled to appear as a witness at the House oversight hearing.

‘‘Where were they before this?’’ he asked of the safety agency. ‘‘The whole relationship is really too cozy. They view their constituency as the auto industry and not the consumer. It’s a classic case of a regulatory agency that over time becomes captured by the industry it regulates.’’