WASHINGTON (AP) _ A congressional study says Medicare rules changes enacted in 1990 helped correct financial inequities hurting rural hospitals.

The Congressional Budget Office study, released Tuesday by Sen. Lloyd Bentsen, D-Texas, tracks the Medicare prospective payment system - which has historically favored urban hospitals over their rural counterparts.

Bentsen, who chairs the Senate Finance Committee, said the study confirms that legislation he pushed, ''has helped rural hospitals, though they still face real financial hurdles.''

But Jim Houdek, a spokesman for the Texas Hospital Association, complained that inequities in payment to rural hospitals have been corrected at the expense of the urban facilities.

''The government didn't really put a lot of new money into the program. They just took it away from urban hospitals,'' he said. ''The reality of it is the system is seriously flawed and continues to be seriously flawed.''

Nationwide, half of the hospitals that have closed in the last decade are urban hospitals, Houdek said. ''The problems are not just rural, the problem is as urban as it can be,'' he said.

Officials of the Health Care Financing Administration, which oversees Medicare, said they had not seen the study and had no immediate comment.

--- Senate Chairman Calls for Release of JFK Files

WASHINGTON (AP) - The chairman of the Senate Intelligence Committee is calling for the release of all classified government files relating to the assassination of President John F. Kennedy.

Sen. David Boren, D-Okla., said in a statement Tuesday that he knew of no indications that the government was involved in any kind of plot in the assassination, ''but it is time to find an appropriate way to clear the air.''

Boren's comments were directed in part at the CIA, which his committee oversees, and came amid renewed discussion of the assassination prompted by the new movie ''JFK''.

''It is important that the American people, particularly those who have been born since the assassination of President Kennedy, have confidence that their own government, even in its most secret programs, is operated in accordance with basic American values,'' Boren said.

--- IRS Wants up to $1.3 Billion from Mobil

WASHINGTON (AP) - The Internal Revenue Service is trying to collect about $300 million in alleged back taxes from Mobile Corp., a figure that could increase by $1 billion in interest if the government is successful.

''The IRS is reconstructing history,'' Mobil Chairman Allen E. Murray said Tuesday in reiterating that the company, based in nearby Fairfax, Va., will fight the tax claim in court.

The IRS assessment grows out of a dispute over the price Mobil charged for some of its imported oil in 1980 and 1981. The IRS has pressed similar claims against Exxon Corp. and Texaco, Inc. - which already have contested the claims in Tax Court - and is auditing Chevron Corp.

The four companies were members of the Arabian-American Oil Co. - Aramco - which bought oil from Saudi Arabia.

After the overthrow of the shah of Iran, Saudi Arabia sold its oil to the big companies at prices below world market levels in an effort to moderate supply disruptions and major price increases.

The IRS contends the four American companies attempted to evade taxes by reselling to their subsidiaries at below-market prices.

''The prices the affiliates actually paid to Mobil were the same as those Mobil paid Saudi Arabia for the crude oil, as mandated by the Saudi government during those years - the so-called 'Aramco advantage,''' Murray said.

''It seems ludicrous to try to punish us for complying with official mandates and the moderate crude price policies of Saudi Arabia, which the U.S. government firmly endorsed,'' he said.

--- FBI Pursuit of Hostage-Takers 'On Hold'

WASHINGTON (AP) - FBI Director William Sessions says the bureau's pursuit of terrorists who held Americans hostage in Lebanon is ''on hold'' pending release of two Germans are still held there.

Sessions arranged a meeting with reporters Tuesday in an effort to minimize discussion of the FBI's efforts.

''We have that on hold,'' he said. ''It is a very, very sensitive area. There still are hostages.''

He said the matter was a subject ''I'd not like to pursue further in public questioning now.''

Last month, FBI chief spokesman Tom Jones said, ''We are investigating in an attempt to determine who the hostage takers are and certainly to have them prosecuted. That's always been one of the objectives of the FBI.''

Since then, law enforcement sources, requesting anonymity, said that bureau officials were advised to temper their public remarks on the investigation at least as long as the Germans remained captive.

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