Can I apply for USA tourist visa when my passport is expiring in 6 months time?

See 9 FAM 403.9-3(B) for passport validity requirements for issuing a nonimmigrant visa.

For passports from countries in the "6-month club", it says that a visa can be issued at any time until the expiration date, though it does mention that if it's too close to expiration it "might not be practical" (9 FAM 403.9-3(B)(2)(b)):

As passports issued by the countries listed in paragraph f below meet the requirements of INA 212(a)(7)(B)(i)(I) until the date shown for expiration, the consular officer could issue a visa at any time prior to that date. However, such action might not be practical when only a very narrow margin of time remains.

For passports from countries not in the "6-month club", 9 FAM 403.9-3(B)(1) says that a visa should only be issued when the passport is valid for 6 months beyond the initial period of stay:

A nonimmigrant visa is only to be issued in passports that are valid for at least six months beyond the initial period of contemplated stay in the United States, except in the following circumstances:

But 9 FAM 403.9-3(B)(3) says that this is not absolutely required, and that a visa can still be issued when the passport is valid for more than 6 months but does not cover the period of stay, if it's not feasible to renew the passport beforehand:

If an applicant presents a passport valid for more than six months but not sufficient to permit admission for the entire period of stay contemplated, the consular officer should urge the applicant to have the passport extended, renewed, or replaced before visa issuance. In the event that this is not feasible until after the alien’s arrival in the United States, the officer may issue the visa. The officer should then advise the applicant that the initial period of stay will be limited because of the limited validity of the passport. The consular officer should also explain the procedures for seeking an extension of stay from the Department of Homeland Security (DHS). Except for aliens covered by the provisions of 9 FAM 403.9-3(B)(2) above, the passport must be valid for more than six months, since an alien presenting a passport valid for six months or less would be inadmissible at a port of entry (POE).

There is a "six-month club" https://www.cbp.gov/document/bulletins/six-month-club-update If your country is on the list, your passport only need to valid for the stay, otherwise it needs to be valid 6 months after your leave.