DISEASE CHARACTERISTICS:

* Histologically or cytologically proven unresectable, locally advanced or metastatic adenocarcinoma of the stomach or gastroesophageal junction
* No known brain metastases

* Negative brain imaging required for neurologic signs and symptoms

PATIENT CHARACTERISTICS:

Age:

* 18 and over

Performance status:

* Zubrod 0-1

Life expectancy:

* Not specified

Hematopoietic:

* Absolute neutrophil count at least 1,500/mm\^3
* Platelet count greater than 100,000/mm\^3

Hepatic:

* Bilirubin no greater than upper limit of normal (ULN)
* SGOT or SGPT no greater than 1.5 times ULN (5 times ULN if liver tumor present)

Renal:

* Creatinine no greater than ULN

Other:

* Not pregnant or nursing
* Fertile patients must use effective contraception
* Must be able to swallow oral medication
* No AIDS syndrome or HIV-associated complex
* No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, or adequately treated stage I or II cancer in complete remission

PRIOR CONCURRENT THERAPY:

Biologic therapy:

* No prior biologic therapy
* No concurrent biologic therapy

Chemotherapy:

* No prior chemotherapy for advanced or metastatic gastric cancer
* At least 6 months since prior chemotherapy as adjuvant or radiation sensitizer

Endocrine therapy:

* Not specified

Radiotherapy:

* At least 1 month since prior radiotherapy and recovered
* No concurrent radiotherapy

Surgery:

* At least 3 weeks since prior major surgical resection of intra-abdominal organs and recovered