WASHINGTON, Oct. 21— The nation's intelligence agencies have experienced a surge in job seekers since the terrorist attacks on Sept. 11, a boom born of lofty patriotism and cold economic realities, recruiters say.

Résumés are pouring in to the Central Intelligence Agency, Defense Intelligence Agency and National Security Agency at a rate four to six times as high as before the attacks.

The applicants range from freshly minted Ph.D.'s in chemical engineering to retired military personnel with foreign-language skills to laid-off high-tech workers eager to join the war on terrorism.

Agency officials say applicants are expressing a desire to help the nation at a time of need. But in the weakening economy, many applicants are also seeking refuge in government jobs.

The overall quality of applicants is good, officials say, and some may fill shortages in the badly depleted ranks of Middle Eastern and Central Asian regional and linguistic experts, as well as technical areas like satellite reconnaissance analysis.

''A lot of patriotic citizens are coming forward wanting to serve, but the economy has also had a bearing on the number of applicants,'' said Frederick G. Wong, a retired one-star Army general who is chief of human resources for the Defense Intelligence Agency.

Congress has already pressed to lift restrictions on the hiring of unsavory foreign agents. But most job seekers sending résumés over the transom are not budding spies. And they appear unswayed by criticisms that the terrorist attacks amount to the worst intelligence lapse since Pearl Harbor.

Before the attacks, the C.I.A. received 500 to 600 job applications a week. The agency is now receiving that many each day, with a peak of nearly 1,100 on Sept. 17, officials said. About 20 percent of the applicants are strong enough on paper to warrant a follow-up phone call, the officials said. Of that 20 percent, about half will probably get a face-to-face interview.

These percentages are roughly the same as before Sept. 11.

''There are always wackos who apply, but we're definitely seeing qualified candidates,'' said Anya Guilsher, a C.I.A. spokeswoman.

The intelligence agencies are receiving most cover letters and résumés online, like this one that the C.I.A. shared on the condition that the applicant's name not be revealed:

''The recent tragedies of Sept. 11 could be prevented if America had stronger intelligence,'' wrote an Iraqi-born New Yorker who recently applied, listing his fluency in Arabic and English, and his proficiency in computer science and information technology, as qualifications.

Last Tuesday, the agency posted on its Web site (www.cia.gov) new job listings for linguists fluent in Arabic, Dari and Pashto, languages spoken in and around Afghanistan. Starting salaries for these and other entry-level positions range from $35,000 to $50,000.

At a career fair on Oct. 12 at Yale University, students stood 10 deep at the C.I.A.'s booth, Ms. Guilsher said. Hundreds of candidates with doctorates in physics, biochemistry and public health, as well as master's degrees in engineering and various foreign languages, left their résumés with recruiters.

At the Defense Intelligence Agency, which employs 7,000 people and provides intelligence to the military, applications have nearly quadrupled from the pre-Sept. 11 rate of 125 to 200 a month.

About 30 percent of the applicants are fresh out of college and the remainder are from both the public and private sectors, General Wong said.

Many applicants are former military personnel, including defense attachés at United States embassies in Middle Eastern and Central Asian countries.

More than two dozen retired D.I.A. specialists are being recalled. In a sign of the urgent need to bring new experts on board, the defense agency has been able to reduce the time needed to conduct security clearances and background checks on candidates to 55 days from four to six months.

Even the National Security Agency, once so secretive that officials jokingly said its initials stood for No Such Agency, has benefited from the outpouring of people interested in shoring up the nation's security and securing a challenging job.

Since Sept. 11, the N.S.A. has received more than 12,000 résumés. In the same period a year ago, agency officials said, it received about 2,200 applications. The agency, which has 15,000 employees, last year hired about 600 people.

''There are still some students who don't know about us, who confuse us with NASA, but interest is very high,'' Ken Acosta, the N.S.A.'s college relations manager, said at a recruiting session at Howard University here last week.

The N.S.A., which is the nation's premier maker and breaker of codes, expects to bring back as many as 100 retired employees, including analysts, linguists and security officials. The agency, which has its headquarters in Fort Meade, Md., is offering $10,000 signing bonuses to qualified computer scientists and engineers.

Applicants to all the intelligence agencies must be American citizens at least 18 years old.

The upswing in applications coincides with revamped recruiting efforts at the intelligence agencies. Three years ago, the C.I.A. beefed up its Internet site and rolled out a new advertising slogan appearing in newspapers and magazines: ''Quite possibly, the most demanding job in the world.''

The Defense Intelligence Agency, under its new director, Vice Adm. Thomas Wilson, increased its advertising budget for recruiting to nearly $400,000 this year from $86,000 a year ago.

''If I go to John Doe in Manhattan, Kan., they have no clue about the D.I.A.,'' General Wong said. ''We don't have that name recognition.''

Résumés are not the only encouraging missives arriving in the mail. The C.I.A. has received a handful of checks, said an agency spokesman, Bill Harlow.

One anonymous benefactor sent his $600 tax rebate check with a simple message: ''Put it toward the cause.''

Photo: Some students confuse his agency with NASA, ''but interest is very high,'' Ken Acosta, a recruiter for the National Security Agency, said during a recruiting visit last week at Howard University in Washington. (David Scull for The New York Times)